Mathieu Castagnet (born 14 November 1986 in Saintes, Charente-Maritime) is a professional squash player who represented France.

In December 2014, he beat the world number one Mohamed El Shorbagy in four games during the British Grand Prix 2014, where he reached the final against Nick Matthew.

1 seed Omar Mosaad in four games, the biggest achievement of his career.

In July 2017, he won the bronze medal at The World Games 2017 in Wrocław, Poland.

This biographical article relating to a French squash figure is a stub.