[1] A senior civil servant in the Inland Revenue Service, Gaillard joined the Resistance and served on its Finance committee.

During the Fourth Republic, he held a number of governmental offices, notably as Minister of Economy and Finance in 1957.

He became Prime Minister in 1957, but, not unusually for the French Fourth Republic; his term of office lasted only a few months.

Gaillard was defeated in a vote of no confidence by the French National Assembly, in March 1958, after the bombing of Sakiet-Sidi-Youssef, a Tunisian village.

Gaillard was last seen alive on 9 July 1970, when he and three passengers boarded his yacht, the Marie Grillon and departed the island of Jersey to return to the French mainland after a brief stay.