Jean-Baptiste Billot entered the École spéciale militaire de Saint-Cyr in 1847, and on leaving it in 1849 joined the staff with the rank of sous-lieutenant.

Billot participated in the Mexico expedition (1861–1867) : commandant of the state of Chihuahua then of Querétaro with the rank of chef d'escadrons (1863, he was mentioned 7 times in dispatches and received the cross of an officer of the légion d'honneur in 1867.

On his return to France, he made a rich marriage and in 1869 was named Chief of staff of the province of Constantine with the rank of lieutenant-colonel.

Billot was elected deputy for Corrèze in 1871 as a member of the Gauche républicaine parliamentary group, before representing this département as "sénateur inamovible" from 1875, sitting among the Republicans.

He was implicated by Émile Zola of conspiracy to frame Alfred Dreyfus, a Jewish officer, for espionage in an 1898 open letter J'Accuse…!.