When the War of the Third Coalition broke out, Harispe served under Marshal Augereau in the Army of the Ocean Coast. In the campaigns of 1805 and 1806, he fought in the Division Desjardin. Harispe was wounded at Jena and in January 1807, he was promoted to general de brigade. Transferred to the corps of Marshal Soult, Harispe was given command of a brigade of the division Verdier. Harispe distinguished himself in fighting at Guttstadt and in the battles of Heilsberg and Friedland, where he was wounded again.