Brenier enlisted in 1786 and gained rapid promotion during the period of the French Revolutionary Wars, becoming an aide-de-camp in 1792 and in 1793 a Chef de brigade (colonel) in the Army of the Eastern Pyrenees (Armée des Pyrénées orientales).

During the Battle of Vimeiro on 20 August 1808, Brenier's brigade made the opening attack against the British held ridge, but it was driven back.

While marching to Brenier's relief, Massena failed to fight his way past Wellington in the Battle of Fuentes de Onoro.

During the pursuit he lost 360 men, but the pursuing British ran into an ambush set by some troops of Jean Reynier's II Corps and the rest of Brenier's soldiers safely reached French lines.

Wellington's forces had just crushed the divisions of Jean Guillaume Barthélemy Thomières and Antoine Louis Popon de Maucune when Brenier's men came up, winded from a rapid march.

Afterwards he took over the command of the city of Brest, where his actions during the Hundred Days earned him a sword of honour voted him by the municipal council.