The son of artist André Masson and brother of the singer and actor Luís Masson, Diego Masson was born in Tossa de Mar, Spain. He studied piano and composition at the Paris Conservatoire. Upon graduation, he joined the Domaine Musical as percussionist and began studying conducting with the group's director, Pierre Boulez.
In 1966 he formed Musique Vivante, a  group specializing in contemporary music which he still directs. Musique Vivante has introduced many important compositions by French and foreign composers, in particular the music of Boulez and Karlheinz Stockhausen. In 1969 Masson conducted the world première of Stockhausen's Stop, which is dedicated to him, and the group also took part in the premières of "Setz die Segel zur Sonne" from Aus den sieben Tagen and the 1972 version of Momente.