At the start of the Peninsular War, Brenier was assigned to Jean Andoche Junot's army for the 1807 Invasion of Portugal. 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. Later General Jean-Andoche Junot ordered Brenier to take his Brigade on a flanking manouvre, he chose to take a even longer route to avoid narrow paths, this made his men arrive late, after Jean-Baptiste Solignac's Brigade had been defeated. Brenier ordered his dragoons forward but they were driven off and the rallying British including the 71st (Highland) Regiment of Foot drive his brigade off with accurate volley fire, which wounded Brenier and led to him being captured by the 71st Regiment. Wounded and captured by the British, he returned to France from captivity in 1809.