He is the only player to have won a title in every age category, including the adult championship since his 2022 victory in finals against Étienne Bacrot.

In 2002, he won his first title in the French under-8 championship in Hyères, in front of Jacques Netzer.

At the under-10 championship in Reims in 2004 he finished behind Stéphane Staatdjian, but won in the same age category the next year in Calvi.

In 2015 in Pau he won his seventh and last French youth championship in the under-20 division, ahead of Pierre Barbot and Raphaël Dutreuil.

Moussard won the silver medal at the World Youth Championships in the Under-10 category in 2004, tied with Yu Yangyi (gold medallist), Hou Yifan (bronze medallist) and Raymond Song (fourth).