After studying at military preparatory high schools in Autun and Aix between 1961 and 1970, Irastorza joined the École spéciale militaire de Saint-Cyr in September 1970.

He graduated in 1972, obtaining the rank of lieutenant and opting for service in the Troupes de marine.

[2] In 1980, promoted to captain, Irastorza was given command of a company of the 8th Marine Infantry Parachute Regiment.

Irastorza then completed his studies and oriented himself towards a high-ranking career by attending the École d'application de l'infanterie, obtaining a Master of Advanced Studies in Defence and international relations in 1986[2] and attending the École supérieure de guerre the next year.

In 1989, he obtained the degree[3] that validates training in command and general staff duties.