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. In the team event, France was overcome by Great Britain in the first round. 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. He was replaced in the team event by Enzo Lefort. He finished the season No.19, his best ranking as of 2014.