He became a miller in 1951, and joined the French Confederation of Christian Workers (CFTC), in order to take part in a strike at his workplace, despite being an atheist.
He then spent a year doing military service, and when he returned to work in 1954, he decided to instead join the General Confederation of Labour's affiliate, the Metalworkers' Federation.
In 1960, he joined the French Communist Party (PCF), and in 1962, he began working full-time for the union's secretariat, focusing initially on electronics workers, and then on the aviation sector.
[1] In 1966, Desmaison was elected as general secretary of the Trade Union International of Workers in the Metal Industry, and spent three years working in Prague.
From 1989, he served on the executive of the CGT, but he retired from all his posts in 1991, after being diagnosed with cancer, and died a few days later.