Guieu commanded a brigade in Jean Sérurier's division during the Montenotte Campaign in April 1796. During the action at San Michele Mondovi on 19 April, his brigade flanked the Sardinians out of position, though the Sardinians later drove the French back when they dispersed to plunder the village. During the Battle of Mondovì on 21 April, Guieu's brigade played a prominent role and helped capture the village of Vicoforte.