As of August 2013, Lemaitre was one of the three Frenchmen (the other two are Ronald Pognon and Jimmy Vicaut) to have broken the 10-second barrier in the 100 metres outdoor.

[7][8] Lemaitre grew up in the town of Annecy, where he took part in handball, rugby and football, before his sprinting prowess was discovered.

[13] He aimed once more at the record at the 2010 European Team Championships and, although he again missed his target, he finished as runner-up against Dwain Chambers with a personal best of 10.02 seconds.

[14] On 9 July 2010, Lemaitre officially became the first man purely of European descent to run 100 metres in under 10 seconds, with a time of 9.98 s at the 2010 French National Championships in the city of Valence.

I will be recognised as the first white man to do so, but today's achievement is mainly about making history for myself!...It is not about the color (of one's skin), it is about hard work.

On 30 July, he appeared to break the 200 metres French national record, but it did not count as the wind speed was 2.3 m/s, which was 0.3 m/s over the limit.

"[31] In the 4 × 100 m relay final, Lemaitre won his first Olympic medal, with his team taking the bronze behind Jamaica (gold) and Trinidad and Tobago (silver).

[33] [34] At the 2014 European Championships, he won three medals, with silvers in the 100 m and 200m behind the British sprinters James Dasaolu and Adam Gemili respectively, before winning bronze in the 4 × 100 m relay.

After a disappointing 2015 season in which he failed to reach the World Championships final in Beijing in either the 100 m or the 200 m, Lemaitre started to think about changing his coach.

However, an injury in June forced him to withdraw from the European Championships in Amsterdam in order to prepare for the Olympic Games.

In the 200 metres final, Lemaitre won the bronze medal in a 20.12 clocking, just 3 milliseconds ahead of Great Britain's Adam Gemili, with the podium spot determined in a photo finish.

[40] Lemaitre was assigned to run the anchor leg for France in the 4 x 100 m final in Doha, but the French team failed to pass the baton on the first exchange and did not finish the race.

[41][42] Lemaitre struggled with injuries in the buildup to the 2020 Summer Olympics and his preparation was further hampered by a bad reaction following a COVID-19 vaccination.

[46] After Lemaitre had first broken the ten seconds barrier in the 100m in 2010, L'Équipe put him on the front page, even though the Tour de France was taking place.

Lemaitre took second place in the total points received that decided who was to win the 2011 men's European Athlete of the Year Trophy.

[47] In addition to his career in athletics, Lemaitre attends the University of Savoy, where he is studying for a professional bachelor's degree in industrial electrical engineering and computer science.