Mekhissi-Benabbad has gained notoriety for pushing the event's mascot after winning the 3000 meter steeplechase finals at the 2010 and 2012 European Championships.
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 metres 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 metres steeplechase competition.
Mekhissi-Benabbad made significant progress in 2008, knocking seconds off his personal best at the 2008 Olympics to win the Olympic 3000 metres 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 metres 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, making him the fourth fastest 3000 metres steeplechaser that year.
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. Another personal best came in the 3000 metres steeplechase at the FBK Games in Hengelo, again behind Brimin Kipruto, as he took second place in 8:06:98. Mekhissi-Benabbad secured a prominent 2009 IAAF Golden League race victory at the Meeting Areva in Paris with a time of 8:13.23. He was selected to represent France at the 2009 World Championships in Berlin, where he was seen as a possible medallist in the 3000 metres 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.
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. Competing in the Reims leg of the French Alma Athlé Tour on 30 June 2010, he beat Bouabdellah Tahri's newly established world record time of 5:13.47 (set only 5 days earlier on 25 June 2010) in the 2000 m outdoor steeplechase. Mekhissi-Benabbad's new world record time of 5:10.68 in that 2000 m outdoor steeplechase race was almost 4 seconds faster than the world record time of 5:14.43 set on 21 Aug 1990 by Julius Kariuki, the Kenyan who would hold the 2000 m outdoor steeplechase world record for almost 20 years until it was broken by Tahri.
Mekhissi-Benabbad won his second consecutive 3000 metres steeplechase Olympic silver medal at the 2012 Olympics in London. In the final, with 200 metres 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. 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.
On 6 July 2013, Mekhissi-Benabbad set a new 3000 metres steeplechase European outdoor record of 8:00.09 in the 3000 metres steeplechase race at the Meeting Areva held in the Stade de France. He beat the previous European outdoor 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 metres steeplechase race, which was won by Ezekiel Kemboi in the world's best time of the year (7:59.03).
Mekhissi-Benabbad won his second consecutive 3000 metres steeplechase World Championships bronze medal at the 2013 World Championships in Moscow. With about 300 metres to go in the final, Mekhissi-Benabbad 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."
At the 2014 European Athletics Championships in Zürich, Mekhissi-Benabbad was disqualified after finishing first in the final of 3000m 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 3000m steeplechase gold medal was awarded to fellow French athlete Yoann Kowal, who had finished second in that race.
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.
Mekhissi-Benabbad won the bronze medal in the 2016 Rio Olympic 3000m steeplechase final. 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.
On 1 July 2012, the Finnish newspaper Karjalainen reported an incident involving Mekhissi-Benabbad at the 2012 European Championships in Helsinki. After winning the 3000 meter steeplechase final, Mekhissi-Benabbad walked over to the championship's mascot “Appy”, which was being worn by a 14-year-old girl, smacked a gift bag out of her hands and pushed her with both hands. He was not fined and did not apologize regarding the incident. That was not the first time that Mekhissi-Benabbad had abused a mascot. After having again won the 3000 meter steeplechase final at the 2010 European Championships in Barcelona, Mekhissi-Benabbad asked a mascot to kneel in front of him before he pushed it to the ground.
On 22 July 2011, immediately after the 1500m race of the Monaco meeting of the IAAF Diamond League, Mekhissi-Benabbad and his fellow competitor and compatriot Mehdi Baala traded blows on the track. The French Athletics Federation handed Mekhissi-Benabbad and Baala a suspension of 10 months each—5 months suspended—from all European Athletics and IAAF track meets. Both were each fined 1500 euros and ordered to perform 50 hours of community service. Mekhissi-Benabbad and Baala were nevertheless cleared to take part in the upcoming 2011 World Championships.All information taken from IAAF profile.