Thomas Gage was born in Firle, Sussex, England, in 1719 or early 1720, to Thomas Gage, 1st Viscount Gage, and his first wife, Benedicta Hall. At eight he entered the Westminster public school, where he studied until 1736. In 1741, he purchased a commission as lieutenant in Colonel Cholmondely's Regiment of Foot. He obtained the rank of captain-lieutenant in May 1742, and became captain in January 1743. Gage served as an aide-de-camp to the Earl of Albemarle; he was present at the Battle of Fontenoy in 1745 and participated in the Battle of Culloden in 1746. He served in Ireland with the 44th Regiment of Foot, and was promoted lieutenant-colonel on March 2, 1751. In the fall of 1754, his regiment was ordered to America under Major General Edward Braddock as part of an effort to counter the French in the Ohio Valley.
Gage and his regiment departed England in early January 1755 and had landed in Virginia by March. He commanded Braddock's advance guard in the march toward the forks of the Ohio River, and led the guard during the defeat at Monongahela on July 9. After the battle, Gage applied for the colonelcy of the 44th, which he did not receive. His regiment spent the winter in Albany, and, after months of inactivity, they set out for Oswego on August 12, 1756, on an expedition to inspect troops, examine forts, and build storehouses along the way. Upon receiving word that Oswego had been attacked, Gage's forces demolished the forts between Albany and Oswego, before retreating down the Mohawk and spending the winter in Albany. During the campaign of 1757, Gage traveled with Loudoun's expedition to attack the French fortress of Louisbourg, but this did not materialize. In December, Gage proposed to Loudoun that a regiment of light infantry specially trained for woodland combat be organized under Gage's command. Loudoun agreed, and formed the 80th Regiment of Light-Armed Foot. Gage set up recruiting headquarters in late December at Brunswick, New Jersey. He reported back to Albany in February 1758 and prepared for the coming campaign. On July 8, 1758,
Gage led the light infantry screen in James Abercromby's failed attack on Ticonderoga, known as the Battle of Carillon. In November, he met with Jeffery Amherst in New York, and there received the news that he had been appointed brigadier general. He continued on to Brunswick and married New Jersey native Margaret Kemble (c.1734--1824) on December 8. They returned to Albany in mid-January 1759, where he took command of Albany and the surrounding forts. Following the siege of Niagara in July, Amherst ordered Gage to take command on Lake Ontario, capture La Galette, and hold that position. Gage refused to take La Galette, focusing instead on strengthening Niagara and Oswego. He was again placed in charge of Albany and its surroundings for the winter of 1759. In 1760, during the final continental campaign, Gage commanded the rearguard in Amherst's army and, in September, Amherst appointed him military governor of Montréal and its surrounding regions, a post he held until October 1763.
In 1761, Gage was promoted to major-general, and in 1762, he received the colonelcy of the 22nd Regiment. When Amherst was granted leave to return to England, Gage was ordered to New York where, on November 17, 1763, he was offered, and accepted, a temporary appointment as commander-in-chief for North America. He was formally commissioned by the King on November 16, 1764. He held the position for twelve years and maintained his headquarters in New York until moving his headquarters to Boston in 1774. In handling Pontiac's Rebellion, Gage approved of Amherst's plan of asking the colonies exposed to Indian attacks to raise 3,500 troops. He also ordered John Bradstreet and Henry Bouquet to move against the Delawares and Shawnees, while William Johnson made peace with Pontiac himself. Political troubles and civil unrest, catalyzed by such legislation as the Sugar and Stamp Acts, necessitated an increase of troops in New York, Philadelphia, and Boston. In the summer of 1768, he ordered the abandonment of many forts along the western, northern, and southern perimeter of the British colonies and indicated in June that only a few posts, including Detroit and Ticonderoga, were necessary to maintain the interior. By March 1769, he wanted troops concentrated on the eastern seaboard. On March 5, 1770, tensions boiled over in Boston, when a group of troops fired into a mob of civilians and killed five citizens. Though this conflict, now known as the Boston Massacre, fostered further mistrust between the citizens and the British troops, the event was followed by a period of relative peace (1771-1772). By 1773, however, the Americans resumed revolutionary activities, unhappy with restrictive Parliamentary acts.
Gage sailed to England upon leave of absence in June 1773. During his time in England, he advised King George III that stronger measures would tame the Americans, and in September met with Lord North and Lord Dartmouth to discuss the problem of addressing French settlement in the American West. He and his wife spent time in Bath and made London their home, until his return to America. The cabinet announced his appointment as governor of Massachusetts on April 2, 1774, replacing Thomas Hutchinson. Gage returned to America, arriving in Boston Harbor on May 13. As the situation became more tenuous, he transferred more troops to Boston. On January 27, 1775, the Earl of Dartmouth sent a secret dispatch to Gage ordering him "to arrest and imprison the principal actors & abettors in the Provincial Congress," the leaders of rebellion. He did not receive this letter until mid-April. Early in the morning of April 19, Gage sent a column to Concord, where the Massachusetts Provisional Congress had met and the rebels held known stores of munitions. The following day, British troops skirmished with militia at Lexington and Concord, before being rescued by a larger brigade sent out by Gage early that morning. On June 12, Gage declared martial law and called a council of war. He decided, along with the recently arrived William Howe, Henry Clinton, and John Burgoyne, to attack the rebels. The British won the Battle of Bunker Hill on June 17, but with a heavy loss of almost forty percent of their troops. Gage received orders on September 26 to return as soon as possible to London, and left Boston on October 10, the same day that Howe became the new commander-in-chief.
On April 13, 1781, Gage accepted a position on Amherst's staff to prepare for the defense of Kent, in case of a possible French invasion. He was made a full general on November 20, 1782. Thomas Gage died in his home in Portland Place, London, on April 2, 1787.