In 1776, the 24th was transferred to Quebec in response to the American invasion, and Governor Guy Carleton promoted him to Brigadier General. When John Burgoyne organized his Saratoga campaign in 1777, Fraser was chosen to command the advance unit. At the start of the campaign, the advance corps had about 1,000 men. Besides his own 24th Regiment of Foot, he had the grenadier battalion, the light infantry battalion, and a company of marksmen, along with some Canadian militia and First Nations auxiliaries. Fraser's command was in the vanguard during the taking of Fort Ticonderoga, and Fraser helped dislodge the retreating Americans.

On 7 July 1777, Fraser's corps caught up with the American rear guard at the town of Hubbardton in the newly formed Republic of Vermont. At the Battle of Hubbardton in a sharp skirmish he drove off the enemy but with the loss of many men.

Early in the Battle of Bemis Heights on 7 October 1777, Fraser fell to rifle fire from Daniel Morgan's rifle brigade. Legend has it that a rifleman named Timothy Murphy was specifically ordered by Benedict Arnold to target Fraser, as he was vigorously directing and supporting his troops. He was carried to a nearby house and placed in the care of Baroness Riedesel, where he died that evening.