By his actions at Pastrengo during the Battle of Verona Grandjean compelled 1,200 Austrians to lay down their weapons. For this exploit he earned a battlefield promotion to general of brigade on 26 March 1799. He led a brigade in the division of Antoine Guillaume Delmas at the Battle of Magnano on 5 April 1799. The division included three battalions each of the 26th, 31st and 93rd Line Infantry Demi-brigades, a grenadier battalion, 1,800 cavalry and a company of foot artillery. The French army commander Barthélemy Louis Joseph Schérer allowed his divisions to fight in isolation. The left flank divisions were successful but Delmas in the center was late to battle and the French right flank divisions were overwhelmed by superior numbers. Schérer conceded victory to the Austrians and began a long retreat.