After having served with the French Navy as a Quartermaster in Indochina and in French Algeria, Denard served as a colonial policeman in Morocco from 1952 to 1957. He worked as a demonstrator for washing machines in Paris. In 1954, he was convicted of an assassination plot against Prime Minister Pierre Mendès-France, a left-wing member of the Radical-Socialist Party who was negotiating the end of the Indochina War and withdrawal from Morocco, Tunisia and Algeria, and served 14 months in jail. An adamant anti-communist, Denard then took part in many anti-colonialist conflicts, simultaneously on his own behalf and on that of the French state. Once he was freed from jail, he worked for the French secret services during the war in Algeria.