Barthel has won four singles and two doubles titles on the WTA tour as well as five singles and one doubles title on the ITF circuit in her career. On 18 March 2013, Barthel reached her best singles ranking of world number 23. On 14 September 2015, she peaked at world number 63 in the doubles rankings.
Mona Barthel was born in Bad Segeberg to Wolfgang Barthel, who won the shot put event at the 1970 European Junior Athletics Championships in Paris, and Dr. Hannelore. She was raised in a tennis-playing family, and took an interest in the game at age 3. She has cited Steffi Graf as an inspiration. Barthel moved to Neumünster, where she completed her Abitur in 2009, having attended the Klaus Groth Schule.
Barthel played her first ITF tournament in July 2007 in Frinton where she qualified for the main tournament and reached the quarterfinals, losing to Jade Curtis. In July 2008, she reached the finals of the Frinton tournament, losing to Tara Moore, and the $10,000 event in Gausdal, losing to Svenja Weidemann. She also reached the doubles final in Gausdal partnering Weidemann, where they lost to Tegan Edwards and Marcella Koek. Her first ITF tournament victory was in January 2010 at the $10,000 ITF tournament in Wrexham, beating Anne Kremer of Luxembourg in straight sets. In February 2010, she reached the doubles final of the $50,000+H Biberach tournament, partnering Carmen Klaschka, losing to Stéphanie Cohen-Aloro and Selima Sfar. In April 2010, she won the singles title at the $50,000 Torhout tournament, beating Rebecca Marino in the final, and also won in doubles, partnering Justine Ozga, defeating Hana Birnerová and Ekaterina Bychkova in the final.
Barthel started 2011 with a tournament victory. In Andrezieux she beat Stephanie Vogt of Liechtenstein. In the summer she won two more titles, in Mestre against Garbiñe Muguruza and in Shrewsbury against Heather Watson. She then played in the 2011 e-Boks Sony Ericsson Open and advanced to her first WTA semifinal, defeating two seeded players en route. In the semifinal she lost to eventual champion Caroline Wozniacki.
Barthel then went on to qualify for the 2011 Wimbledon Championships without dropping a set in the qualifying rounds.
Barthel started her year at the ASB Classic in Auckland. She defeated Jelena Dokić in the first round, but lost a close match against compatriot Sabine Lisicki in round two.
Barthel qualified for the Moorilla International in Hobart. She defeated Romina Oprandi in the first round, and followed it up with three upsets in a row, beating second seed Anabel Medina Garrigues, fifth seed Jarmila Gajdošová, and fourth seed Angelique Kerber. In the final, she defeated top seed Yanina Wickmayer to claim her first WTA title. With this win, Barthel became the first qualifier since September 2010 to win a WTA tournament.
Following her maiden title win, Barthel made her debut at the Australian Open. In the first round she defeated Anne Keothavong and number 32 seed Petra Cetkovská. In the third round she was defeated by the third seed and eventual champion Victoria Azarenka.
Her next tournament was the 2012 Open GDF Suez in Paris. In order to play in the main draw, Barthel had to qualify, which she did successfully by defeating Mariya Koryttseva, Julie Coin and Varvara Lepchenko. In the first round of the main draw she defeated Barbora Záhlavová-Strýcová. In the secound round she crushed Frenchwoman Pauline Parmentier to move into the quarterfinals, but then lost her quarterfinal match to Yanina Wickmayer.
In Doha, Qatar, she reached the second round, but lost to new world number 1 Victoria Azarenka. After passing her opening round in Indian Wells at the BNP Paribas Open, she was drawn to verse Azarenka again, a match in which she played the best tennis of her career as she led 4–1 in the third set and served for the match twice but eventually lost. After a comprehensive victory over Gréta Arn at the Sony Ericsson Open in Miami, Barthel defeated 13th seed and former number 1 Jelena Janković before losing in the third round to another in-form unseeded opponent, Ekaterina Makarova.
As the sixth seed at the e-Boks Sony Ericsson Open in Copenhagen, Barthel beat Johanna Larsson and Alberta Brianti to reach the quarterfinals where she lost to second seed and fellow German Angelique Kerber despite leading in the final set and holding match points.
Barthel was given a wildcard into the 2012 Porsche Tennis Grand Prix in her home country. In the first round she defeated former world number 1 and French Open Champion Ana Ivanovic. In the second round, Barthel recorded her first victory against a top 10 player by defeating world number seven and seventh seed in her biggest career win to date, Marion Bartoli. She played world number 1 Victoria Azarenka for the fourth time that year, losing in three sets. Barthel reached the semifinals of the Swedish Open in Båstad, losing to Polona Hercog.
At her first Olympic Games, Barthel lost to Urszula Radwańska. Barthel then travelled to the Rogers Cup in Montreal, and beat Tímea Babos in a third set tiebreak before dropping a match point against second seed Agnieszka Radwańska, falling in three sets. At the US Open, Barthel lost to Bojana Jovanovski in the first round.
After reaching the semifinals of the ASB Classic and the final of the Hobart International, Barthel won her second WTA title and first premier title at the Open GDF Suez in Paris, where she defeated Sara Errani in straight sets. This win moved Barthel up to 28 in the world rankings. Barthel's next tournament was at the Qatar Total Open, where she beat Yulia Putintseva in the first round and took out the 5th seed Angelique Kerber in straight sets. She lost in the third round to Caroline Wozniacki in straight sets. At the Premier Mandatory event in Indian Wells, Barthel made it to the fourth round, including wins over Kiki Bertens and former world number 1 and 11th seed Ana Ivanovic. She lost to Samantha Stosur in the fourth round. After this tournament, her ranking rose to a career high of world number 23.
Barthel started her clay court season by participating at the 2013 Family Circle Cup, where she was seeded 8th. After receiving a bye into the first round, she lost to American Jessica Pegula, despite serving for the first set. Representing Germany for the first time, Barthel travelled to Stuttgart to play the Fed Cup World Group Play-off. In her first match she lost to Ana Ivanovic in three sets but beat Bojana Jovanovski to bring the tie all-square at 2–2. After Sabine Lisicki and Anna-Lena Grönefeld beat the Serbian doubles team, it secured Germany their place in the 2014 Fed Cup World Group.
Barthel then played at the indoor clay event in Stuttgart but lost in the first round to Lucie Šafářová. In doubles she partnered with fellow German Sabine Lisicki where they beat experienced players, Bethanie Mattek-Sands and Sania Mirza in the final. This was Barthel's first doubles title.
Barthel's next tournament was the 2013 Mutua Madrid Open where she lost to Kirsten Flipkens in the first round. She had to withdraw the Premier 5 tournament in Rome, due to a stomach illness. At the second Grand Slam of the year in Paris, she lost to Angelique Kerber in the first round, despite having set points in the first set tie-break. Mona's scheduled tournaments for the grass court season were in Birmingham, 's-Hertogenbosch and Wimbledon. She lost to young American and Madison Keys in Birmingham and Garbiñe Muguruza in 's-Hertogenbosch. At the 2013 Wimbledon Championships, Barthel advanced to the second round for the first time in her career, but was again on the losing end to Keys.
To kick off the summer hardcourt season in North America, Barthel's first tournament was the 2013 Citi Open where she was seeded 6th. She beat Switzerland's Stefanie Vögele in the first round but lost to the eventual finalist Andrea Petkovic in the second round. In Toronto she reached the second round but lost to Sloane Stephens in three sets. She had a good preparation for the US Open in Cincinnati where she defeated Lucie Šafářová and upset Maria Kirilenko. She faced Serena Williams in her next match but lost in round three. At the last Grand Slam of the year in New York, Barthel made it to round two where she lost to Alison Riske. In doubles, she partnered up with Līga Dekmeijere where they reached the second round, losing to the 16th seed pairing of Jelena Janković and Mirjana Lučić-Baroni.
During the Asian swing, Barthel suffered early losses to Venus Williams in Tokyo, Lauren Davis in Beijing, Elina Svitolina in Linz and Vögele in Luxembourg to end her paradoxical season.
Barthel started her season at the 2014 ASB Classic where she was a semifinalist the previous year. Seeded 7th, she lost in the 1st round to Yvonne Meusburger of Austria 6-4, 6-3. She then travelled to Hobart for the 2014 Hobart International where she reached the final the year before. Seeded 6th, she defeated Elina Svitolina in the 1st round 6-4, 6-3. In the 2nd round, she lost to Monica Niculescu 7-6(5), 6-1. At the 2014 Australian Open, Barthel defeated Shuai Zhang in the 1st round 7-6(4), 6-3. In the 2nd round, she beat Luksika Kumkhum 4-6, 6-3, 6-4. In the 3rd round, she lost to eventual quarterfinalist and 28th seed Flavia Pennetta 6-1, 7-5 despite serving for the second set at 5-4.
Barthel went to Paris to defend her title at the 2014 Open GDF Suez, but she lost in the 1st round to 8th seed Kirsten Flipkens 6-3, 4-6, 6-2. With this loss, Barthel dropped from 36 to 64 in the world rankings. Barthel added further disappointment to her season with a 1st round loss at the 2014 Qatar Total Open to compatriot Annika Beck 7-6(5), 6-2. She also lost in the final round of qualifying at the 2014 Dubai Tennis Championships to Maryna Zanevska 7-6(8), 6-4. At the 2014 BNP Paribas Open, Barthel lost in the 1st round to Francesca Schiavone 3-6, 6-2, 6-2. At the 2014 Sony Open Tennis, Barthel faced Rebecca Peterson in the 1st round. Barthel retired down 4-6, 2-4 due to gastrointestinal illness. Playing at the 2014 BNP Paribas Katowice Open for the first time, she lost in the 1st round to fellow German Annika Beck 6-1, 6-4 for the second time in two months.
The following week, Barthel was the 5th seed for qualifying at the 2014 Porsche Tennis Grand Prix. She reached the qualifying round where she lost to 3rd seed Ajla Tomljanović 6-4, 5-7, 7-6(1). However, she got a Lucky Loser spot in the main draw. In the 1st round, Barthel lost to 5th seed Jelena Janković 2-6, 7-6(8), 6-3 even though she had several match points against the Serb. Barthel then lost in the 2nd round of qualifying at the 2014 Portugal Open to Kiki Bertens 6-3, 6-3 and at the 2014 Mutua Madrid Open to Petra Cetkovská 6-4, 6-4.
Barthel successfully qualified for the 2014 Internazionali BNL d'Italia defeating 1st seed María Teresa Torró Flor 6-1, 6-2 and 14th seed Virginie Razzano 6-3 ret. In the 1st round, she lost to 13th seed Carla Suárez Navarro 6-2, 6-2. Before the French Open, Barthel competed at the 2014 Nürnberger Versicherungscup. In the 1st round, she defeated Belinda Bencic 7-6(4), 6-3. In the 2nd round, she beat 8th seed and compatriot Annika Beck 6-2, 6-4 before losing in the quarterfinals to 4th seed Elina Svitolina 6-4, 6-4. Barthel had a good run at the 2014 French Open, defeating Karin Knapp in her opener 6-4, 6-0. She advanced to the 3rd round when compatriot and 16th seed Sabine Lisicki was forced to retire with a wrist injury at 6-1, 3-0. In the 3rd round, she lost to French wildcard Pauline Parmentier 1-6, 6-1, 7-5.
At the 2014 Aegon Classic, Barthel defeated Ajla Tomljanović in the 1st round 6-1, 6-4 before falling to top seed and eventual champion Ana Ivanovic in the 2nd round 6-4, 6-1. The following week, she qualified for the 2014 Topshelf Open beating Dinah Pfizenmaier 7-6(6), 6-2 and 7th seed Urszula Radwańska 6-3, 6-2. In the 1st round, she defeated Maria Kirilenko 6-3, 6-2. In the 2nd round, she lost to 8th seed Klára Koukalová 6-2, 7-6(6). At 2014 Wimbledon Championships, Barthel beat Romina Oprandi in the 1st round 7-5, 6-0. In the 2nd round, she lost to 6th seed and eventual champion Petra Kvitová 6-2, 6-0.
At the 2014 Gastein Ladies, she lost to 8th seed Karolína Plíšková in the 1st round 6-4, 6-4. The following week, she competed at the 2014 Swedish Open. She defeated qualifier Tereza Martincová in the 1st round 6-4, 6-4. In the 2nd round, she defeated Gabriela Dabrowski 6-4, 3-6, 6-4. In the quarterfinals, Barthel beatKaia Kanepi 6-2, 7-6(4). In the semifinals, Barthel defeated Sílvia Soler Espinosa 6-2, 4-6, 7-5. In the final, Barthel defeated Chanelle Scheepers 6-3, 7-6(3) to win her 3rd WTA Title. Barthel moved back into the world's top-50 after this result.
Barthel began her US Open Series by playing qualifying at the 2014 Western & Southern Open. She, as the 4th seed, reached the qualifying round by beating wildcard Yulia Putintseva 6-4, 6-2. She lost to 18th seed and compatriot Annika Beck in the final round of qualifying 6-2, 6-3. However, due to Azarenka's withdrawal, Barthel got a lucky loser spot into the main draw. In the 1st round, she lost to Barbora Záhlavová-Strýcová 7-5, 6-0. Barthel then played qualifying at the 2014 Connecticut Open. Again, as the 4th seed, she won the 1st two rounds of qualifying defeating Kiki Bertens 7-6(4), 3-6, 7-5 and Jana Čepelová 3-1 ret. In the final round of qualifying, Barthel lost to 11th seed Belinda Bencic 6-3, 7-6(6). At the 2014 US Open, Barthel defeated 32nd seed Shuai Zhang in the 1st round 6-1, 6-2. She lost in the 2nd round to American Varvara Lepchenko 6-4, 6-0.
After the US Open, Barthel played at the 2014 Korea Open. She beat 7th seed Caroline Garcia in the 1st round 7-6(3), 6-2. She then lost in the 2nd round to Christina McHale 6-1, 4-6, 6-3. At the 1st edition of the 2014 Wuhan Open, Barthel defeated Peng Shuai in the 1st round 6-2, 7-6(1) before losing in the 2nd round to 6th seed and eventual finalist Eugenie Bouchard 4-6, 6-3, 6-4. Barthel, as the 5th seed, successfully qualified for the 2014 China Open defeating Misaki Doi 6-4, 2-6, 6-4 and Marina Erakovic 6-3, 6-3. In the 1st round, she beat fellow qualifier Bethanie Mattek-Sands 4-6, 6-1, 6-4. In the 2nd round, Barthel lost to 13th seed Lucie Šafářová 6-3, 6-3. At the 2014 Generali Ladies Linz, Barthel defeated lucky loser Kiki Bertens in the 1st round 6-3, 6-1 before losing in the 2nd round to 7th seed and eventual champion Karolína Plíšková 6-4, 6-2.
Barthel's final tournament of the year was at the 2014 BGL Luxembourg Open. She defeated wildcard Mandy Minella in the 1st round 6-3, 6-4. In the 2nd round, she beat 8th seed and two time finalist Monica Niculescu 0-6, 7-5, 6-3. In the quarterfinals, she defeated Kiki Bertens 6-3, 6-0 to reach the semifinal. In the semifinal, she fell to 4th seed Barbora Záhlavová-Strýcová 6-3, 6-2.
Barthel ended the year ranked 43.
During her preparation for 2015, Barthel suffered a torn ligament in her right foot.
Barthel began the year at the 2015 ASB Classic. Seeded 8th, she lost in the 1st round to Ana Konjuh 6-2, 6-1. She then traveled to Hobart for the 2015 Hobart International. Seeded 7th, she lost in the 1st round to qualifier and eventual finalist Madison Brengle 6-7(6), 7-5, 7-6(2). At the 2015 Australian Open, Barthel defeated Donna Vekić in the 1st round 3-6, 6-4, 6-2. In the 2nd round, she lost to 4th seed Petra Kvitová 6-2, 6-4.
After the Australian Open, Barthel competed at the 2015 Diamond Games. In the 1st round, she beat qualifier Klaartje Liebens 6-2, 6-0. In the 2nd round, Barthel upset 1st seed Eugenie Bouchard 4-6, 6-1, 6-2. In the quarterfinals, Barthel lost to Barbora Záhlavová-Strýcová 6-2, 6-2. Barthel then lost in the 1st round at the 2015 Dubai Tennis Championships to wildcard Daniela Hantuchová 7-6(5), 3-6, 6-3. As the 2nd seed for qualifying at the 2015 Qatar Total Open, she lost in the 1st round of qualifying to Kateryna Kozlova 6-2, 6-2. At the 2015 BNP Paribas Open, Barthel defeated Kristina Mladenovic in the 1st round 6-3, 5-7, 6-4. In the 2nd round, she lost to 10th seed Lucie Šafářová 6-4, 7-6(4). Barthel then had a 1st round exit at the 2015 Miami Open, losing to Bojana Jovanovski 3-6, 6-3, 6-2.
Barthel began her clay court season at the 2015 Family Circle Cup in Charleston, South Carolina. Seeded 15th, she defeated Tímea Babos in the 1st round 6-3, 6-3 and American Sloane Stephens in the 2nd round 6-3, 7-6(2). In the 3rd round, she retired against American Lauren Davis at 6-4, 3-0 due to dizziness. After Charleston, Barthel competed at the 2015 Porsche Tennis Grand Prix. She lost in the 1st round to wildcard and compatriot Carina Witthöft 7-5, 6-3. At the 2015 Grand Prix SAR La Princesse Lalla Meryem, Barthel lost in the 1st round to eventual finalist Tímea Babos 6-4, 6-0. She lost in the 1st round at the 2015 Mutua Madrid Open to qualifier Christina McHale 6-3, 6-2. At the 2015 Internazionali BNL d'Italia, Barthel was defeated in the 1st round by 10th seed and eventual finalist Carla Suárez Navarro 6-4, 2-6, 6-3. Her final tournament before the French Open was the 2015 Internationaux de Strasbourg. In the 1st round, she faced French wildcard Virginie Razzano. Barthel retired down 6-2, 5-5 due to a wrist injury. At the 2015 French Open, Barthel lost in the 1st round to qualifier Paula Kania 5-7, 6-2, 6-4.
Barthel missed the 2015 Aegon Open Nottingham and the 2015 Aegon Classic due to a wrist injury. Barthel only played one grass court tournament before Wimbledon, the 2015 Aegon International. She lost in the 1st round to eventual champion Belinda Bencic 6-4, 7-6(7). At the 2015 Wimbledon Championships, Barthel lost in the 1st round to Anastasia Pavlyuchenkova 6-7(3), 7-6(4), 6-2.
After Wimbledon, Barthel competed at the 2015 Swedish Open where she was the 4th seed and defending champion. She defeated Kiki Bertens in the 1st round 6-7(4), 6-2, 6-3. In the 2nd round, Barthel crushed qualifier Maryna Zanevska 6-0, 6-0. In the quarterfinals, she beat Swedish wildcard Rebecca Peterson 6-1, 7-6(3). In the semifinal, she defeated Lara Arruabarrena 6-3, 6-2 to reach the final for a 2nd year in a row. In the final, Barthel lost to 7th seed and Sweden's Johanna Larsson 6-3, 7-6(2). At the 2015 İstanbul Cup, Barthel defeated qualifier Olga Savchuk 6-3, 7-5 in the 1st round. In the 2nd round, she lost to qualifier Kateryna Bondarenko 6-3, 4-6, 6-2.
Barthel began her US Open Series competing at the 2015 Bank of the West Classic. She reached the quarterfinals by defeating wildcard Carol Zhao 6-3, 6-0 and 6th seed and compatriot Andrea Petkovic 5-7, 6-2, 7-6(4). In the quarterfinals, Barthel lost to American Varvara Lepchenko 6-7(3), 6-2, 6-3. At the 2015 Rogers Cup, Barthel lost in the final round of qualifying to Anna Tatishvili 6-3, 6-3. Barthel successfully qualified for the 2015 Western & Southern Open by defeating Elena Vesnina 6-1, 6-2 and 22nd seed Irina Falconi 6-4, 6-1. In the 1st round, she defeated qualifier Casey Dellacqua 2-6, 6-3, 7-6(4). In the 2nd round, she lost to Sloane Stephens 3-6, 7-6(1), 6-2. Barthel reached the 3rd round at the 2015 US Open for the first time by beating Tsvetana Pironkova 5-7, 7-6(4), 6-1 and Olga Govortsova 2-6, 6-2, 6-4. In the 3rd round, she lost to Varvara Lepchenko 1-6, 6-3, 6-4.
As the 3rd seed at the 2015 Coupe Banque Nationale, Barthel lost in the 1st round to eventual finalist Jeļena Ostapenko 7-6(6), 4-6, 6-4. Barthel, as the 5th seed, reached the quarterfinals at the 2015 Korea Open defeating wildcard Jang Su-jeong 6-0, 7-6(2) and Mariana Duque Mariño 6-2, 6-1. She lost in the quarterfinals to 2nd seed Anna Karolína Schmiedlová 6-4, 3-6, 6-1. Barthel then lost in the 1st round of qualifying at the 2015 Wuhan Open to Patricia Maria Țig 6-4, 6-2.
At the 2015 China Open, Barthel beat Chinese wildcard Shuai Zhang in the 1st round 6-3, 6-2. In the 2nd round, she lost to 4th seed Agnieszka Radwańska 4-6, 6-1, 6-4. At the 2015 Generali Ladies Linz, Barthel defeated qualifier Kiki Bertens in the first round, 7-5, 3-6, 6-2 before losing in the 2nd round to qualifier Aleksandra Krunić 7-6(6), 6-3. At her final tournament of the year, the 2015 BGL Luxembourg Open, Barthel reached the final defeating 6th seed Sloane Stephens, Tatjana Maria, Mirjana Lučić-Baroni, and wildcard Stefanie Vögele. In the final, Barthel lost to Misaki Doi 6-4, 6-7(7), 6-0. However, in doubles, Barthel and fellow German Laura Siegemund defeated Spaniards Anabel Medina Garrigues and Arantxa Parra Santonja in the final, 6-2, 7-6(2). This was her second WTA title in doubles.
Barthel ended the year ranked 44.
Barthel began her year at the 2016 ASB Classic. In the 1st round, she faced 4th seed Svetlana Kuznetsova. Barthel retired trailing 2-6, 1-1 due to illness. Seeded 9th at the 2016 Hobart International, she defeated World Number 65 Misaki Doi in the 1st round 6-4, 6-4. In the 2nd round, Barthel suffered a back injury, but she still managed to beat qualifier Naomi Osaka 7-6(2), 6-2. She withdrew from her quarterfinal match against 7th seed Alizé Cornet due to the back injury. At the 2016 Australian Open, Barthel was defeated in the 1st round by World Number 349 Vania King 3-6, 7-5, 6-4.
Barthel missed St. Petersburg, Qatar, Indian Wells, Miami, Charleston, Prague, and Nuremberg due to health problems.
Barthel returned at the 2016 French Open. She lost in the 1st round to World Number 63 Irina Falconi 6-4, 0-6, 6-2.
Barthel began her grass court season at the 2016 Aegon Open Nottingham. Seeded 7th, she lost in the 1st round to World Number 89 and eventual finalist Alison Riske 6-2, 6-1. She then withdrew from the 1st edition of the 2016 Mallorca Open and the 2016 Aegon International Eastbourne due to illness. At the 2016 Wimbledon Championships, she defeated World Number 52 Danka Kovinić in the 1st round 6-2, 7-6(3). In the 2nd round, Barthel lost to 26th seed Kiki Bertens 6-4, 6-4.
After Wimbledon, Barthel competed at the 1st edition of the 2016 Ladies Championship Gstaad. Seeded 7th, Barthel was defeated in the 1st round by World Number 105 and eventual champion Viktorija Golubic 2-6, 6-1, 7-5. Playing at the 2016 Swedish Open, Barthel was leading 4-6, 6-3, 3-0 in her 1st round match against 7th seed Yaroslava Shvedova when Shvedova retired due to a back injury. In the 2nd round, Barthel lost to World Number 85 Karin Knapp 6-0, 7-5.
Playing qualifying at the 2016 Western & Southern Open, Barthel lost in the 1st round of qualifying to 5th seed Daria Gavrilova 6-0, 6-4. At the 2016 Connecticut Open, Barthel lost in the 2nd round of qualifying to Camila Giorgi 6-2, 6-2. At the 2016 US Open, Barthel lost in the 1st round to World Number 55 Christina McHale 6-2, 6-2.
Seeded 6th at the 2016 Coupe Banque Nationale, Barthel was defeated in the 1st round by Canadian wildcard Françoise Abanda 7-6(7), 6-4. At the 2016 Korea Open, Barthel had her first WTA main draw win since Bastas by beating 7th seed Nicole Gibbs in the 1st round 5-7, 6-4, 6-2. She lost in the 2nd round to Camila Giorgi 2-6, 6-1, 6-4. Playing at the 2016 Generali Ladies Linz, Barthel was defeated in the 1st round by 4th seed Carla Suárez Navarro 6-4, 6-2. Last year finalist at the 2016 BGL Luxembourg Open, Barthel lost in the 2nd round to 8th seed Johanna Larsson 6-1, 6-4. As a result, Barthel failed to defend her finalist points from last year. Her ranking dropped from 135 to 190. At the 2016 Internationaux Féminins de la Vienne, Barthel lost in the 2nd round to Alison Van Uytvanck 6-1, 6-3. Competing at the 2016 Open de Limoges, she was defeated in the 1st round by 8th seed Stefanie Vögele 6-3, 6-4. Barthel played her final tournament of the year at the 2016 Al Habtoor Tennis Challenge in Dubai. She reached the semifinals defeating 3rd seed Evgeniya Rodina, Nina Stojanović, and Ivana Jorović. In the semifinals, she lost to 5th seed and eventual champion Hsieh Su-Wei 3-6, 7-5, 6-1.
Barthel ended the year ranked 183.
Barthel began her season by playing in the qualifying rounds at the 2017 ASB Classic. She qualified for the main draw beating 2nd seed Magda Linette, wildcard Joanna Carswell, and 8th seed Dalila Jakupović. In the 1st round, she lost to Mirjana Lučić-Baroni 6-3, 3-6, 6-3. At the 2017 Apia International Sydney, Barthel was defeated in the 1st round of qualifying by 6th seed Danka Kovinić 6-1, 1-6, 6-4. Barthel successfully qualified for the 2017 Australian Open beating 15th seed Richèl Hogenkamp, Teliana Pereira, and 8th seed Maryna Zanevska. In the main draw, Barthel reached the 4th round at the Australian Open for the first time in her career after having wins over wildcard Destanee Aiava, 29th seed Monica Puig, and wildcard Ashleigh Barty. In the 4th round, Barthel lost to 13th seed and eventual finalist Venus Williams 6-3, 7-5. Nevertheless, this was Barthel's beat result at the Australian Open. Her ranking improved from 181 to 111.
At the 2017 Qatar Total Open, Barthel lost in the 1st round of qualifying to 4th seed Kristýna Plíšková 1-6, 6-3, 6-2. Receiving a wildcard to play at the 2017 Dubai Tennis Championships, Barthel beat Jelena Janković in the 1st round 6-1, 6-3. In the 2nd round, she was defeated by top seed and compatriot Angelique Kerber 6-4, 6-3. Qualifying for the 2017 BNP Paribas Open, Barthel was defeated in the 1st round by Kateřina Siniaková 4-6, 6-4, 6-4. At the 2017 Miami Open, Barthel lost in the 2nd round of qualifying to 21st seed Taylor Townsend 7-6(6), 6-3.
Barthel began her clay court season at the 2017 Volvo Car Open. She beat American Jennifer Brady in the 1st round 7-5, 6-4. In the 2nd round, Barthel lost to 11th seed Mirjana Lučić-Baroni 6-3, 6-2. Next, Barthel competed at the 1st edition of the 2017 Ladies Open Biel Bienne. She won her 1st round match over Jana Čepelová 6-3, 6-4. In the 2nd round, she lost to Elise Mertens 6-2, 6-4. Seeded 3rd for qualifying at the 2017 J&T Banka Prague Open, Barthel qualified for the main draw beating Sachia Vickery, Jasmine Paolini, and 8th seed Denisa Allertová. In the 1st round, she beat 6th seed Shuai Zhang 6-0, 6-3. In the 2nd round, she defeated Océane Dodin 6-3, 6-1. In the quarterfinals, Barthel defeated Camila Giorgi 7-6(0), 7-6(6). In the semifinals, Barthel beat 3rd seed Barbora Strýcová 3-6, 6-2, 6-3 to advance to her first WTA singles final since 2015. In the final, Barthel defeated Kristýna Plíšková 2-6, 7-5, 6-2 to win her 4th WTA singles title and her first WTA singles title since 2014. After the tournament, her ranking went from 82 to 56. Barthel qualified for the 2017 Internazionali BNL d'Italia defeating Maria Sakkari and Varvara Lepchenko. In the 1st round, she beat Peng Shuai 6-1, 3-6, 6-3. In the 2nd round, she defeated qualifier Wang Qiang 6-3, 6-4. In the 3rd round, Barthel lost to 8th seed and eventual champion Elina Svitolina 3-6, 6-0, 6-0. Ranked 50 at the 2017 French Open, Barthel was defeated in the 1st round by Tsvetana Pironkova 6-0, 6-4.
Barthel began her grass court season at the 2017 Aegon Open Nottingham. Seeded 7th, Barthel lost in the 1st round to qualifier Jana Fett 6-3, 5-7, 7-5. At the 2017 Mallorca Open, Barthel lost in the 2nd round to Catherine Bellis 4-6, 6-4, 6-2. Seeded 2nd for qualifying at the 2017 Aegon International Eastbourne, Barthel made it to the main draw beating Beatriz Haddad Maia and Kristína Kučová. In the main draw, she was defeated in the 2nd round by 7th seed Svetlana Kuznetsova 4-6, 7-5, 6-2. Ranked 48 at the 2017 Wimbledon Championships, Barthel lost in the 1st round to 24th seed Coco Vandeweghe 7-5, 6-2.
Seeded 4th at the 2017 Ladies Championship Gstaad, Barthel was defeated in the 1st round by Maria Sakkari 4-6, 6-3, 6-3. At the 2017 Swedish Open, Barthel upset 9th seed Johanna Larsson in the 1st round 6-7(3), 7-5, 7-6(4). She lost in the 2nd round to qualifier Kateryna Kozlova 6-3, 6-3.
Barthel began her US Open Series at the 2017 Rogers Cup. Seeded 4th for qualifying, she lost in the 1st round of qualifying to Mariana Duque Mariño 1-6, 6-4, 6-4.
Barthel plays aggressively, and is primarily known for her power and movement. She is noted for having a strong serve and for hitting shots down the line, as well as for a tendency to approach the net. In her straight-sets victory at the 2013 GDF Suez, she hit 53 winners. Barthel produces deep groundstrokes, and hits powerfully on both the forehand and backhand sides.
On defense, she is noted for her aggressive return of serve, as well as for her scrambling ability.