2011–15 Gemili won a silver medal over 100 m at the
2011 European Athletics Junior Championships in
Tallinn,
Estonia. He also helped the British squad to a silver medal in the 4 × 100 m relay. At the National Junior Athletic League Finals, Gemili won the 200 m in 20.98 s, which was the fastest time by a European junior in 2011. Gemili ran an Olympic qualifying time for the 100 m and won the Sparkassen Gala in
Regensburg, Germany on 2 June 2012, just over three weeks prior to the British track trials for the
2012 London Olympics. behind only
Dwain Chambers (10.06 s). At the time of his victory,
James Dasaolu was the only one other British athlete to have met the Olympic qualifying time for the men's 100 m. Besides breaking the British national junior record, Gemili's time ranked second among European juniors (behind
Christophe Lemaitre's 10.04 s) and sixth all-time among all juniors, behind only Brown,
Jeffery Demps,
Marcus Rowland,
D'Angelo Cherry and Lemaitre. Gemili competed at the
2012 London Olympics where he, after a poor start, came third in the semi-final in a time of 10.06 s, 0.04 s short of qualifying for the final. He qualified to run the 200 m at the
2013 World Championships in Athletics in
Moscow. Having set a personal best in the first round, in the semi-final Gemili ran a time of 19.98 s, making him only the second British athlete, after
John Regis, the third teenager (after
Usain Bolt and
Alonso Edward), and the ninth European athlete, to break 20 seconds in the event. 2013 was his first season training for the event. He thus qualified for his first major final where he finished fifth with a time of 20.08 s. in
Zürich. Gemili won his first senior medal at the
2014 Commonwealth Games coming second to Jamaica's
Kemar Bailey-Cole in the
100 m final in a time of 10.10 s. Two weeks later, Gemili took his first senior title, winning the 200 m at the
2014 European Athletics Championships, in an equal personal best of 19.98 s (−1.6 m/s).
2015–19 On 31 May 2015, he broke the
10-second barrier in the 100 m for the first time in his career, with a run of 9.97 seconds, but the wind speed was above the legal
wind limit. Two months later, on 7 July at the
Diamond League meeting in Birmingham, he became the 100th man in history to break the 10-second barrier legally, again clocking 9.97 seconds . He fell as he crossed the line, picking up a hamstring injury which caused him to miss the
2015 World Championships. Gemili qualified for the
men's 200 m final at the
2016 Rio Olympics. He, Christophe Lemaitre, and
Churandy Martina were separated by six thousandths of a second. The
photo finish showed Lemaitre to be the bronze medalist, with Gemili in fourth. He was overlooked for individual selection for the 2017 World Championships, following early season injury, but was included in the 4 × 100 m relay team. Racing both heats and final, he won a historic gold medal as a member of the British quartet in a national and European record, lifting the team to third on the all-time list behind USA and Jamaica. The final was also notable as
Usain Bolt's last race; third at the changeover, he pulled up injured and was unable to finish. Gemili qualified for both the individual 100 m and 200 m at the
2019 World Athletics Championships in
Doha, Qatar. He was eliminated in the 100 m at the semi-final stage, missing out on qualification for the final via a photo finish. He narrowly missed out on a medal in the 200 m final, leading the race coming off the bend but ultimately finishing in fourth place. He ran the first leg of the men's 4 × 100 m relay, winning a silver medal behind the United States in a new European record time of 37.36 seconds. Off track, in November 2019 Gemili led a group of 20 British athletes including
Mo Farah,
Katarina Johnson-Thompson and
Laura Muir who threatened to take legal action against the
British Olympic Association regarding the interpretation of the
International Olympic Committee's
Rule 40 contained in guidelines which had been recently issued by the association. Rule 40 restricts use of Olympic-related terms in marketing by non-approved sponsors: the athletes argued that the BOA's interpretation of the rule was too restrictive regarding how they could promote their individual sponsors. In March 2020 the athletes reached an agreement with the BOA which would allow athletes more opportunities to promote their sponsors during and immediately before and after the Games. In July 2020, Gemili was announced as a board member of the track and field athletes' union, the Athletics Association. ==Football career==