He served under his father during the Williamite War in Ireland, fighting against the Jacobite Irish Army. Frederick Schomberg was second in command of William's army at the Battle of the Boyne in July 1690. Meanwhile, Meinhardt Schomberg commanded the right wing of William's army during the battle and led the crucial crossing of the River Boyne at Roughgrange near Rosnaree on the Jacobites' flank, the turning point in the confrontation, despite a gallant defence by Sir Neil O'Neill, a Jacobite general. Schomberg then engaged in a pursuit of the retreating troops towards Duleek: there were no casualties amongst his regiment's soldiers. Schomberg's father died during the latter stages of the Battle which resulted in a decisive Williamite victory.