Bradstreet's early military service consisted of garrison duty in Nova Scotia with the 40th Regiment of Foot, during which time he took advantage of his Acadian heritage and engaged in trade with the French at Louisbourg.

He survived but his warnings to Governor Shirley and Lord Loudon of the weak condition of Fort Oswego were largely ignored in midst of their ongoing power struggle.

After the failed attempt to capture Ticonderoga, Bradstreet immediately proposed his idea to attack Fort Frontenac, the key French supply base on Lake Ontario.

Under the new British commander in North America, Jeffery Amherst, Bradstreet served as deputy quartermaster general in Albany, a lucrative position which he held until the end of the war.

His superiors considered Bradstreet to have mismanaged his final campaign; exceeding his orders by attempting to negotiate independent peace treaties and failing to act aggressively enough against Pontiac's forces.

Bradstreet is often remembered today for his work organizing and leading a corps of armed boatmen and teamsters in the British service, tasked with moving supplies and troops along the inland waterways of upstate New York and the Great Lakes.