Drafted into the French armed forces in 1939, Casanova was promptly taken prisoner; however, he escaped and resumed contact with the party through an intermediary, Claudine Chomat, in March 1942.

He was Minister for Veterans and War Victims in the provisional governments of Félix Gouin and Georges Bidault from 26 January to 8 July 1946.

He represented the party in the Peace Movement, replacing Charles Tillon, who stepped down in 1952 (in connection with his association with André Marty).

However, Thorez managed to block the "aggiornamento" (trend to "bring things up to date") and eliminated Casanova from all governing bodies in May 1961.

Philip Robrieux devotes a few pages in his monumental biography of Maurice Thorez (4 volumes) to "The Inside Story of the French Communist Party" (V.2, p. 499–503 and V. 4, p. 126–127)