With expiring enlistments leaving fewer than 100 men remaining in his regiment, Haslet crossed the Delaware with Washington and joined the attack at the Battle of Trenton on the morning of December 26, 1776. However, on January 3, 1777, in a skirmish at the beginning of the Battle of Princeton, with General Hugh Mercer down and wounded, Haslet tried to rally Mercer's brigade and was himself shot in the head and killed instantly. Nevertheless, they did rally and a surprising victory was won to complement the earlier one at Trenton. The "corps of loyalists" he defeated at Mamaroneck was led by the famous Indian fighter Robert Rogers (soldier). Legend has it that Washington wept over his corpse on the battlefield and notes by Washington's stepson confirm that Washington did come across Haslet's body at Princeton, but does not mention any shedding of tears.