Mertine climbed in 2010 his first World Cup podium with a bronze medal in Copenhague, and was selected into the France national team as a reserve.

[4] In the 2012–13 season, he earned a bronze medal in the Seoul World Cup and in the Tokyo Grand Prix, but ceded to Belarus' Siarhei Byk in the first round of the European Championships in Zagreb.

At the World Championships in Budapest Mertine defeated Great Britain's Richard Kruse in the first round, but was then beaten by Heo Jun of South Korea.

In the 2013–14 season Mertine won the national French championships after defeating successively Enzo Lefort and Erwann Le Péchoux.

[9] In the team event France defeated Russia in the semi-finals and proceeded to crush China to earn the world title.