Lagaillarde was a lawyer at Blida in Algeria, a reserve officer of the paratroopers, and an elected deputy of Algiers.
Lagaillarde was then detained in La Santé Prision in Paris, and while imprisoned, he was visited by Jean-Marie Le Pen.
He took advantage of his parole to escape to Spain (along with Jean-Jacques Susini, Jean-Maurice Demarquet, Marcel Ronda [fr] and Fernand Féral Lefevre), where he was joined by Raoul Salan and co-founded the Organisation armée secrète on 3 December 1960.
Deprived of his immunity as a deputy, he was sentenced in absentia to ten years of prison in March 1961.
[2] The Spanish dictator, Francisco Franco, later exiled Lagaillarde to the Canary Islands.