He was a cadet at the École Spéciale Militaire de Saint-Cyr 1905 to 1907 (promotion "la Dernière du vieux Bahut").

As part of Brigadier Harold Rawdon Briggs' Briggsforce, Free French forces participated in the East African campaign.

In November Legentilhomme was condemned in his absence for treason by the Government of Vichy and sentenced to the death penalty.

[citation needed] In 1942 he was awarded the Compagnon de la Libération cross by General Charles de Gaulle on 9 September 1942, and became High Commissioner of the French possessions in the Indian Ocean as well as Governor-General of Madagascar and general Officer Commander in Chief Madagascar.

In 1943 he became a member of the Empire Defense Council, and was nominated to be Lieutenant General and Commissaire to the French Committee for National Liberation.

In 1952 he was technical advisor of the Minister François Mitterrand (who much later was President of the French Republic between 1981 and 1995).

For 1952 to 1958 he was member of the Assemblée de l'Union française for the UDSR political party (in French).