Duckworth was born in Sydney, New South Wales. He attended Sydney Church of England Grammar School, where he was on the school tennis first team from Year 7 and went on to win several AAGPS Premierships. He was offered a scholarship to the Australian Institute of Sport. where he was able to further develop his tennis. Duckworth is a keen supporter of the Newcastle Knights in the National Rugby League.
Duckworth played his first ITF under-18 tournament in December 2005 as a 13-year-old, the event was held in Perth and Duckworth lost in the first round to Sebastian Bell. Duckworth's first big result came in December 2007 when he made his first final in Manila, Philippines but had to retire in the third set against Francis Casey Alcantara. Duckworth's first title came in August 2010 at the Oceania Closed Championship held in Fiji, he beat fellow Australian Maverick Banes in the final. Out of the nine junior tournaments Duckworth entered in 2010 he managed to reach three finals that resulted in two titles won in Kuching, Malaysia and Manila, Philippines respectively. Duckworth's best junior result came at 2010 Roland Garros Junior Championships where he reached the semifinals. He reached as high as No. 7 in the combined world rankings in July 2010.
Duckworth entered his first professional tournament in September 2006 as a 14-year-old in Happy Valley, South Australia where he was defeated in the first round of qualifying. He entered his second pro tournament in September 2007; the event was held in Sawtell, New South Wales, and Duckworth made it to the final round of qualifying, but fell at the last hurdle. In November 2008, Duckworth received a wildcard into a Futures tournament held in Perth and made the most of his opportunity; he recorded his first main draw victory in the first round. He followed up the victory with a surprise win over the fifth seed. In the quarterfinals, he fell to fourth seed and eventual champion Andrew Coelho. The following week, Duckworth received another wildcard into an event held in Sorrento, Western Australia, but could not keep the form going as he fell in the first round to James Lemke. Despite entering four Australian Futures toward the end of 2009, Duckworth only won one match and finished 2009 ranked no. 1712.
The 2010 season began for Duckworth with a qualifying wildcard into his hometown ATP event in Sydney where he lost in the first round to fellow Australian Marinko Matosevic 1–6 3–6. He also received a wildcard into the qualifying tournament of the 2010 Australian Open but fell in the first round to Somdev Devvarman 2–6 1–6. While not competing in junior tournaments Duckworth played several futures tournaments held in Australia, Netherlands, USA and New Zealand. His best result came in November when he reached the semifinals of a futures tournament held in New Zealand. Duckworth finished the year ranked 742 in the ATP rankings.
Duckworth, long time friends with James Duff and Max Coleman began the year playing in the 2012 Brisbane International and the 2012 Australian Open qualifying tournaments after receiving wildcards into each event. Following the Australian summer series of tournaments Duckworth headed to Europe in hopes of boosting his ranking. Duckworth's choice of tournaments would prove successful with four titles and two runners-up in tournaments held across Poland and Italy.
His latest futures title was in Este Padova where he defeated Australian Jason Kubler en route to the final against Daniele Giorgini. These results have enabled him to enter the top 300 and is now also one of Australia's top 10 players. Duckworth capped off the year by reaching the final of the 2012 Australian Open Men's Wildcard Playoff, falling to Marinko Matosevic 6–4 6–1 6–2.
Following a successful 2011 season Duckworth was granted main draw wildcards into the Brisbane International, Apia International Sydney and the Australian Open. In the first round of the 2012 Brisbane International Duckworth drew Frenchman Nicolas Mahut. After trailing 0–4 in the first set Duckworth came back and won his first ever ATP match 6–4 6–4. In the second round of Brisbane Duckworth fell to world no. 12 Gilles Simon 3–6 5–7 on Pat Rafter Arena. In the 2012 Apia International Sydney Duckworth fell to qualifier and eventual champion Jarkko Nieminen 2–6 2–6. On his Grand Slam debut Duckworth drew Estonian Jurgen Zopp in the first round, Duckworth came out victorious in straight sets 6–3 6–4 6–4. In the second round Duckworth faced world number 9 Janko Tipsarević and got off to a quick start taking the first set. Duckworth would eventually lose in four sets 6–3 2–6 6–7 4–6. Following the Australian Open Duckworth entered the Burnie Challenger where he was a first round casualty to Ben Mitchell 6–4 3–6 4–6. A week later Duckworth was seeded third in the Caloundra challenger and lived up to his seeding by reaching his first ever challenger semifinal. He was defeated by eventual champion Marinko Matosevic in the semifinals 6–7 3–6.
Duckworth started his year at the 2013 Brisbane International where he lost in the second round of qualifying. He then played in the 2013 Apia International Sydney, where as a wildcard he almost made an upset against world number 46 Denis Istomin 7–6(4), 4–6, 6–7(3). Duckworth then played in the 2013 Australian Open after receiving a wild card. He defeated fellow Australian and good friend Ben Mitchell in the first round 6–4, 7–6(8), 4–6, 5–7, 8–6. He then played another long five set match in the second round, losing to world number 93 player Blaž Kavčič 6–3, 3–6, 4–6, 7–6(3), 8–10. After two first round losses against James Ward at the 2013 McDonald's Burnie International and the Charles Sturt Adelaide International, Duckworth reached the final of the Australia F1 Futures in Melbourne going down against Stephane Robert 6–7(3), 3–6. Duckworth then competed in the 2013 Nature's Way Sydney Tennis International losing to compatriot Samuel Groth in the quarterfinals 6–7(2), 6–7(5).
Duckworth reached the second round at the 2013 All Japan Indoor Tennis Championships after defeating Jose Rubin Statham 6–4, 4–6, 6–3. He went down to second seed Marco Chiudinelli 6–7(5), 7–6(7), 2–6. Duckworth returned to Australia to compete in the Australia F5 tournament in Bundaberg. He reached the final and won it defeating Jason Kubler 7–6(9), 6–2. This was his fifth ITF title and his first in Australia.
After qualifying, Duckworth lost to Blaž Kavčič in round 1 of the 2013 French Open. At Wimbledon, Duckworth progressed through qualifying again, but lost in the first round to fellow qualifier Denis Kudla in 5 sets. In October, Duckworth made the semi finals of Melbourne Challenger, which improved his ranking to a career high of 132.
Duckworth started his year at the 2014 Brisbane International after being awarded a wildcard. He was defeated in round 1 by Jarkko Nieminen
On 8 January, Duckworth was awarded a wild card into the 2014 Australian Open. His first round opponent was Roger Federer. He lost in straight sets.
In April, Duckworth reached the final of the Cachantún Cup. This was his second Challenger final, but lost to Thiemo de Bakker. Duckworth qualified for the 2014 French Open but lost in round one to Leonardo Mayer. In June, Duckworth qualified for the 2014 Aegon Championships and made round 2, where he lost in a close three set match against the #2 seed, Tomáš Berdych, 4-6 in the third set. Duckworth qualified for 2014 Wimbledon Championships and in round 1, lead Richard Gasquet 2 sets to 1, before ultimately losing in 5.
In July, Duckworth competed in the Lexington Challenger where he defeated countrymen Jordan Thompson in round 2 and Thanasi Kokkinakis in the semi final. He defeated Brit James Ward, 6-3, 6-4 in the final. This was his first Challenger Title.
Duckworth was beaten in round 2 of qualifying at the US Open. In November, Duckworth made the final of the Charlottesville Challenger. He defeaed Brit Liam Broady in the final on 2 November, this was his second career challenger tour. Duckworth finished 2014 with a career high ranking of No.127.
As with the previous three years, Duckworth commenced his season at the 2015 Brisbane International after being awarded a wild card. In round 1, he caused an upset, defeating world no.21 Gilles Simon, 6-2 6-2. He then defeated Jarkko Nieminen reaching the quarter-finals in an ATP Tour event for the first time in his career. But then he lost to Roger Federer in straight sets 0-6,1-6. Duckworth was given a wild card into the 2015 Australian Open, where he defeated Blaž Kavčič in round 1 but lost to the 24th seed Richard Gasquet in the second round. In February, Duckworth was the no.1 seed at the Delhi Challenger and Kolkata Challenger. He lost in round 2 at Delhi and lost in the final of Kolkata to Radu Albot. At Indian Wells, Duckworth qualified and defeated Dominic Thiem in round 1 before losing to Fernando Verdasco, as a result of his performance, he secured a top 100 ATP ranking for the first time in his career. Duckworth then qualified for the 2015 Miami Open and reached the second round where he again lost to Verdasco. He then returned to the challenger tour playing in San Luis, Anning and Bordeaux where he lost in the semi-finals, quarter-finals and second round respectively. Duckworth then played in the Tour 250 event in Nice where he defeated lucky losers Frances Tiafoe and Quentin Halys to reach his second ATP tour quarterfinal of 2015 and his career. He then lost to Borna Ćorić in straight sets. At Wimbledon, Duckworth came back from 2 sets to 0 down again Malek Jaziri to win in five sets, posting his first win at Wimbledon. He lost to compatriot Sam Groth in round 2. At the US Open, Duckworth lost in round 1 to Hyeon Chung in straight sets. He played a number of challenger events to finish the season making the quarter finals in Ho Chi Minh, Ningbo and Knoxville. Duckworth ended the year with a ranking of 120.
Duckworth again commenced the year at the 2016 Brisbane International, but lost in round 1 to Dominic Thiem. He played doubles with Chris Guccione where they made the final losing to Henri Kontinen and John Peers. Duckworth was awarded a wild card into Sydney, where he defeated Íñigo Cervantes and lost to Jérémy Chardy in round 2. At the 2016 Australian Open, Duckwork lost to Lleyton Hewitt in round 1. Duckworth tore a flexor tendon in his right elbow after the Australian Open, he then broke his left wrist doing sprints and sidelined Duckworth for four months. His ranking dropped to outside the top 200. He returned to play in May and won the China F6 in Wuhan and Bangkok Challenger. Duckworth's grass season was unsuccessful, winning just one match in qualifying. In July, Duckworth qualified for the main draw at the 2016 Citi Open, losing in the second round to the number 1 seed, John Isner. Duckworth lost in the final round of qualifying for Rogers Cup and again in Atlanta Open, both in final set tie-breaks. At the US Open, Duckworth was awarded a wild-card. He defeated Robin Haase in round 1. In November, Duckworth won his second and third Challenger titles of the year, defeating compatriot and maiden finalist Marc Polmans in Canberra and Tatsuma Ito in Japan. Duckworth ended the year with a ranking of 103.
Duckworth commenced the season at the 2017 Australian Open where he received direct entry for the first time in his career. He lost to Paolo Lorenzi in round 1.