Thomas Gage was a younger son of the first viscount Gage. He entered the army and served in Flanders, 1747-1748, as aide de camp to Lord Albemarle, and in 1751 became lieutenant colonel of the 44th Regiment, one of two regiments of regulars sent to America under General Braddock late in 1754. Gage led the advanced detachment on Braddock's march toward Fort Duquesne and was wounded in the rout of that expedition. Subsequently he was employed at Oswego. In 1758 he raised a regiment of light infantry, designated the 80th. He was married the same year to Margaret Kemble, daughter of a member of the New Jersey Council. He served under Abercromby in the attack on Fort Ticonderoga and later was stationed at Crown Point as a brigadier general. After the capture of Fort Niagara in 1759 Gage succeeded Sir William Johnson as commander in that region and led the rear guard of the army under Amherst which moved on Montreal and forced the capitulation of Canada in 1760. He remained at Montreal as governor for three years, rising in rank to major general.

When Amherst returned home in November 1763 the command of the troops in America devolved on Gage, who went immediately to headquarters in New York. Although peace had been signed with France, Gage found an Indian uprising raging in the West under Pontiac. He sent out two punitive expeditions under Colonels Bradstreet and Bouquet and then left peace negotiations to Sir William Johnson, the superintendent of Indian affairs in the North. He reestablished only two of the nine posts which had fallen to the Indians. In 1765 he finally got troops into Fort Chartres on the Mississippi. Gage divided his command into three districts--northern, southern, and western--with a brigadier in command of each. His officers were scattered in posts from Halifax and St. Johns to Pensacola and Mobile and westward to the Mississippi. After the repeal of the Stamp Act, peacetime administrative duties occupied him, except for the excitement after the Boston Massacre on March 5, 1770.

In June, 1773, Gage visited England on leave, General Haldimand commanding in his absence. He returned in May, 1774, with the additional title of governor of Massachusetts. He moved his headquarters to Boston, and his first task was to keep the port closed in punishment for the Tea Party. Friction increased, an illegal Provincial Congress was set up, and Gage's attempt to seize rebel ordnance hidden at Concord provoked the initial skirmish of the Revolution in April, 1775. Late in May reinforcements arrived to assist Gage, including three major generals -- Howe, Clinton, and Burgoyne. The costly battle of Bunker Hill resulted only in the British being shut up in Boston under siege. With no further campaign in sight for that year Gage was called home in August and sailed in October. The command in America was split between Howe and Carleton. Gage was inactive during the rest of the war, but died a full general.