2004-2007

Mekhissi-Benabbad made his first appearances as a junior athlete in 2004, running at the 2004 IAAF World Cross Country Championships, where he was 61st in the junior race, and at the 2004 World Junior Championships where he was eliminated in the heats of the 3000 m steeplechase. He ran in the 1500 metres event at the 2006 European Cup, where he finished eighth. Mekhissi-Benabbad represented France at the 2006 IAAF World Cup, but only managed to finish eighth in the 1500 m event.

Mekhissi-Benabbad won the 3000 m steeplechase gold medal at the 2007 European Athletics U23 Championships. He competed in his first major senior event later that year – the 2007 World Championships - where he was eliminated in the heats of the 3000 m steeplechase competition.

2008

Mekhissi-Benabbad made significant progress in 2008, knocking seconds off his personal best at the 2008 Olympics to win the Olympic 3000 m steeplechase silver medal in a time of 8:10.49, only 15 hundredths of a second behind the gold medallist Brimin Kipruto. He became the first non-Kenyan in 24 years to finish first or second in the Olympic 3000 m steeplechase event. Coincidentally, the last non-Kenyan to do so was a Frenchman—Joseph Mahmoud—who won the silver medal at the 1984 Olympics in Los Angeles. Mekhissi-Benabbad improved further at the 2008 Weltklasse Zürich meeting, finishing behind Paul Kipsiele Koech in second place in a personal best time of 8:08.95,^[5] making him the fourth fastest 3000 m steeplechaser that year.^[6]

2009

Mekhissi-Benabbad opened the 2009 season with an appearance in the 3000 metres event at the Qatar Athletic Super Grand Prix, where he registered a personal best of 7:53.50.^[7] Another personal best came in the 3000 m steeplechase at the FBK Games in Hengelo, again behind Brimin Kipruto, as he took second place in 8:06:98.^[8] Mekhissi-Benabbad secured a prominent 2009 IAAF Golden League race victory at the Meeting Areva in Paris with a time of 8:13.23.^[9] He was selected to represent France at the 2009 World Championships in Berlin, where he was seen as a possible medallist in the 3000 m steeplechase. But he failed to complete his heat in that event when he was forced to step off the track injured with just over a lap to go.^[10]

2010

Mekhissi-Benabbad took part in the 2010 World Indoor Championships, his first major indoor competition, where he reached the final of the 1500 m and finished in eighth position with a time of 3:45.22. During the outdoor season of 2010, he scored a steeplechase win in 8:08.82 over Ezekiel Kemboi and Richard Mateelong at the Meeting International Mohammed VI d'Athlétisme de Rabat.^[11] Competing in the Reims leg of the French Alma Athlé Tour on 30 June, he broke Bouabdellah Tahri's newly established world best of 5:13.47 (set only 5 days earlier on 25 June) in the 2000 m steeplechase. Mekhissi-Benabbad's new world best of 5:10.68 was almost 4 seconds faster than the mark of 5:14.43 set on 21 Aug 1990 by Julius Kariuki, the Kenyan who would hold the 2000 m steeplechase world best for almost 20 years until it was broken by Tahri.^[12]

2012

Mekhissi-Benabbad won his second consecutive 3000 m steeplechase Olympic silver medal at the 2012 Olympics in London. In the final, with 200 m in the race remaining, Ezekiel Kemboi was in the lead, followed by Abel Kiprop Mutai in second place, Roba Gari in third place and Mekhissi-Benabbad in fourth place. Mekhissi-Benabbad then swept past both Gari and Mutai to finish second behind Kemboi. "I want to congratulate Ezekiel Kemboi because he won and it is not by chance because he won in 2004. ... He is stronger than me, but I do hope one day I can beat him," Mekhissi-Benabbad said right after the race.^[13] Right after the race, Kemboi did the victory dance he had become known for. He and Mekhissi-Benabbad exchanged jerseys and the diminutive Kemboi leaped into the much larger Mekhissi-Benabbad's arms.

2013

On 6 July 2013, Mekhissi-Benabbad set a new 3000 m steeplechase European record of 8:00.09 in the race at the Meeting Areva held in the Stade de France. He beat the previous European record of 8:01.18 set in Berlin at the 2009 World Championships by his compatriot Bouabdellah Tahri. Mekhissi-Benabbad finished second in that Meeting Areva 3000 m steeplechase race, which was won by Ezekiel Kemboi in the world's best time of the year (7:59.03).^[14]

Mekhissi-Benabbad won his second consecutive 3000 m steeplechase World Championships bronze medal at the 2013 World Championships in Moscow. With about 300 metres to go in the final, he passed Ezekiel Kemboi, then Paul Kipsiele Koech and became jointly in the lead with Conseslus Kipruto. Just after clearing the third-last hurdle in the final bend, Kemboi saw his chance and surged forward to pass both Mekhissi-Benabbad and Kipruto. From then on, Kemboi never relinquished his lead. Kipruto overtook Mekhissi-Benabbad at the start of the final straight and eventually finished second behind Kemboi. Right after the race, Mekhissi-Benabbad admitted that he was finding it hard to cope with the pressure. "In the French team I am under a lot of stress and pressure, but I have to deal with it the best I can. ... I had to settle for bronze again but it is never easy to win one. I am on the podium and that is what counts."^[15]

2014

At the 2014 European Athletics Championships in Zürich, Mekhissi-Benabbad was disqualified after finishing first in the final of 3000 m steeplechase. The action was taken after he removed his shirt on the home-straight of the final lap in an act of celebration, and the Spanish team lodged an official protest for "unsporting behaviour". The 3000 m steeplechase gold medal was awarded to fellow French athlete Yoann Kowal, who had finished second in that race.^[16] Mekhissi-Benabbad would win the 1500m title three days later.

2015

In early April 2015, Mekhissi-Benabbad underwent an operation on his right foot, which had been causing him pain, in a hospital in Qatar. As he needed several months to recover from his operation, he was forced to miss the 2015 summer athletics season, including the 2015 World Championships in Beijing.^[17]

2016

Mekhissi-Benabbad won the bronze medal in the 2016 Rio Olympic 3000 m steeplechase final.^[18] Having crossed the line in fourth place, he controversially filed a complaint against Ezekiel Kemboi who had finished third. Kemboi was judged to have committed a lane violation, resulting in his disqualification.^[19]