Jaziri reached his highest individual ranking on the ATP Tour of world no. 50 in October 2016. He appeared in the qualifying draw at the 2010 Australian Open, losing in the first round to Michał Przysiężny of Poland. He primarily plays on the Futures circuit and the Challenger circuit. Jaziri qualified for the 2011 US Open, defeating Brian Dabul, Michael Ryderstedt, and Guillaume Rufin in the qualifying draw. This was the first time Jaziri played in the main draw of a Grand Slam tournament. In the first round, Jaziri defeated world no. 159 Thiemo de Bakker in four sets. Jaziri lost to world no. 8 Mardy Fish in the second round. Jaziri has been coached by Tunisian legend Haythem Abid on and off throughout his career.
In 2012, he kicked off his year at the ATP 250 event in Doha and pushed world no. 6 Jo-Wilfried Tsonga to three sets in the first round. He fell in the first round of qualifying at the Australian Open to Tim Smyczek. He then reached three Challenger finals in Quimper, Kyoto, and Pingguo to break into the top 100 for the first time.
In his clay season, he made the semifinals in the Barletta Challenger and played his first Roland Garros main draw, winning his first-round match over German Philipp Petzschner before losing a tight second-round match to Spaniard Marcel Granollers, missing two match points.
On grass, he reached the second round in his Wimbledon debut (lost to Kohlschreiber) and also the second round at the London Olympics (lost to John Isner).
He lost in the US Open first round, but later had his best result on the ATP World Tour when he reached the semifinals of the Kremlin Cup in Moscow (lost to eventual champion Andreas Seppi) to become the first Tunisian male to reach the semifinals of an ATP event.
In 2013, Jaziri started off the year in Dubai, where he faced 17-time Grand Slam champion, Roger Federer and lost in three tight sets.
Jaziri started off 2015 making his first appearance at the Australian Open main draw, and beating Kazakhstan's Mikhail Kukushkin and France's Edouard Roger-Vasselin, making him the first Arab male tennis player to make it to the third round of a Grand Slam in over a decade. Jaziri then lost in the third round to Australian teen Nick Kyrgios.
Jaziri has been a member of the Tunisia Davis Cup team since 2000, posting an 18–12 record in singles and a 7–10 record in doubles in 29 ties.
Jaziri was embroiled in a controversial political incident, in which he withdrew from a tournament rather than play an Israeli player. In the October 2013 Tashkent Challenger, tournament in Tashkent, Uzbekistan, he was slated to play Israeli Amir Weintraub in the quarterfinals. But the Tunisian tennis federation ordered Jaziri by email to withdraw from the match, and he did so.
Weintraub said that Jaziri is "a good friend," and that "he really wanted to play." Israel Tennis Association CEO Shlomo Glickstein said: "It is sad to me that these kinds of things still happen. I feel bad for the athletes who find themselves embroiled in such situations, which end up hurting their careers.”
Jaziri was cleared of wrongdoing by the ATP, but the International Tennis Federation (ITF) found that the Tunisian Tennis Federation breached the ITF constitution by ordering him not to compete. The organization barred Tunisia from competing in the 2014 Davis Cup. ITF president Francesco Ricci Bitti said: "There is no room for prejudice of any kind in sport or in society. The ITF Board decided to send a strong message to the Tunisian Tennis Federation that this kind of action will not be tolerated by any of our members."
In February 2015, Jaziri was again embroiled in a controversial political incident when he withdrew from a tournament before facing Israeli players. He withdrew from both the singles and doubles events at the Open Sud de France, citing an elbow injury, after winning his first set in his singles match against Denis Istomin of Uzbekistan. Had Jaziri won, he would have been scheduled to face Israeli Dudi Sela in the next round. In the doubles event, he and Spanish partner Marc López would have faced Israeli opponent Jonathan Erlich and František Čermák of the Czech Republic in the quarterfinals.
The ATP said that they had confirmed with on-site medical staff that Jaziri's elbow injury was genuine, but opened an inquiry, stating: "Given a previous incident involving the player's national federation in 2013, we are looking into any wider circumstances of his withdrawal as a matter of prudence." On February 10, the ATP closed its investigation after extensive discussions with Jaziri and medical staff, saying it was satisfied that Jaziri had a legitimate medical reason to retire from the event.