At the age of 20, Lemaitre won the 100 m, 200 m and the 4×100 m relay titles at the 2010 European Championships, the first French sprinter ever to achieve that triple. He was the fastest European 100 m and 200 m sprinter in 2010. He won a bronze medal in the 200 m at the 2011 World Championships. 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.