Thomas Bryan Martin (1731–1798) was an 18th-century English American land agent, justice, legislator, and planter in the colony (and later U.S. state) of Virginia and in present-day West Virginia. Martin was the land agent of the Northern Neck Proprietary for his uncle Thomas Fairfax, 6th Lord Fairfax of Cameron (1693–1781) and served two terms in the House of Burgesses. Martin was born in Kent in 1731, and was the grandson of Thomas Fairfax, 5th Lord Fairfax of Cameron (1657–1710) through his mother, Frances Fairfax Martin. Raised in humble surroundings in England, Martin relocated to Virginia in 1751 to assist his uncle, Thomas Fairfax, 6th Lord Fairfax of Cameron (known as Lord Fairfax), in administering the Northern Neck Proprietary, which encompassed up to . Martin resided with his uncle on their frontier Greenway Court estate in present-day Clarke County, Virginia. He earned the affections of Lord Fairfax on account of his energetic nature and loyalty, and through Martin's growing influence Lord Fairfax relocated the proprietary's base of operations to Greenway Court in 1762 and made Martin steward and land agent of the proprietary. Martin took an active role in political and civil affairs within the proprietary's domain. He served as a vestryman for the Anglican Frederick Parish, and upon the creation of Hampshire County in 1754, he presided as the county's first justice and was further appointed the County Lieutenant. He later represented Hampshire County in the House of Burgesses from 1756 to 1758 and serving with George Washington, represented Frederick County from 1758 until 1761. Martin was appointed a trustee of the frontier towns of Winchester, Stephensburg (present-day Stephens City), and Bath (present-day Berkeley Springs). He was also appointed as the colonel of the Frederick County militia. Though not in the best of health, Martin was relied upon by the settlers of the proprietary to use his considerable resources in response to Native American attacks. Following the outbreak of the American Revolutionary War, Martin refused reappointment by Governor Patrick Henry as a justice of the Frederick County Commission of Peace. Afterward, Martin retreated from civil service entirely, and retired to Greenway Court. He maintained a low profile during the war, and his uncle Lord Fairfax was treated with respect and consideration despite being the only resident peer in the American colonies. Following the death of Lord Fairfax in 1781, Martin's brother Reverend Denny Martin Fairfax inherited the Northern Neck Proprietary,