He transferred to the Army of Italy in 1796 and was present at the battles of Dego, Mondovì, Lodi, Bassano, and Arcole.

In 1800 he fought at Montebello and Marengo as an aide-de-camp to Claude Perrin Victor.

In 1806 Thomières joined the staff of Marshal Jean Lannes and served in Prussia and Poland.

He was promoted to general officer in July 1807 and participated in the 1807 invasion of Portugal.

Thomières led a brigade at Corunna, Bussaco, and Fuentes de Oñoro before being appointed to head a division.