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.
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.
[11][12] The proprietary constituted up to 5,000,000 acres (20,000 km2) of Virginia's Northern Neck and a vast area spanning west to the North Branch Potomac River headwaters.
[11][13][14] In 1750, Martin's uncle Lord Fairfax established himself at his hunting plantation Greenway Court estate near present-day White Post in Clarke County with the intention of administering the proprietary himself.
[8] He soon earned the affections of Lord Fairfax on account of his energetic nature, his loyalty, and his good eyesight, which greatly assisted his myopic uncle.
[8] On May 21, 1752, shortly after Martin had come of age on his twenty-first birthday, Lord Fairfax granted Greenway Court to his nephew, along with 8,840 acres (35.8 km2) of limestone lands on the west bank of the Shenandoah River across from Leeds Manor, which were "to be known and called by the name of the Manor of Greenway Court" and subject to an annual quit-rent fee of "a good buck and doe" due on the feast day of Saint Michael the Archangel.
[13] At Martin's suggestion, Lord Fairfax relocated the proprietary's base of operations 56 miles (90 km) northwest from Belvoir to an expressly built land office depository and archive at Greenway Court in 1762.
"[20] Martin's uncle Robert Fairfax remarked on the primitive life at Greenway Court among "strange, brutish people... past all conception".
[20] For the next thirty years, until Lord Fairfax's death in 1781, Martin remained at Greenway Court and shared in the loneliness and solitude of his "self-exiled" uncle.
"[22] In addition to his management of the proprietary, Martin began taking an active role in political and civil affairs within his uncle's domain.
[4][27] In 1758, Martin and George Washington challenged the incumbents and ran for election to represent Frederick County in the House of Burgesses against Hugh West and Thomas Swearingen.
[28][29] Martin and Washington received considerable support from Lord Fairfax, and the leading Anglican cleric in Frederick County, William Meldrum.
[34] His uncle Lord Fairfax, John Hite, Gabriel Jones, Robert Rutherford, Lewis Stephens, and James Wood were also appointed trustees of the towns alongside Martin.
[4][37] While Martin was not in the best of health, he could be relied upon by the settlers of the proprietary to use his considerable resources to act promptly during an emergency, especially in response to attacks by Native Americans.
[39] Martin was reappointed as a justice of the peace by Governor Patrick Henry, along with William Booth and Warner Washington, but all three men declined to serve another term.
[39][40][41] Martin did not swear into the committee because he refused to serve under the new revolutionary regime, initially believing that American independence from Great Britain was a futile effort.
[20] By 1778, the Virginia General Assembly had abolished quit-rents, but in recognition of Lord Fairfax's loyalty, the Northern Neck Proprietary was made an exception.
[20] Lord Fairfax was treated with respect and consideration by the assembly, and despite being the only resident peer in the American colonies, he was accorded all the privileges of a Virginia citizen.
[44] Martin also inherited the plantation Lord Fairfax had purchased from John Borden consisting of 600 acres (2.4 km2), the Greenway Court estate and "all the stock of cattle, sheep, hogs, implements of husbandry, household goods and furniture" there.
[13] As required in Virginia, they placed newspaper advertisements telling proprietary tenants to bring their claims against the Lord Fairfax estate forward and prove them.
[24][43] Powers also inherited "all houses thereon, household goods (except plate and watch), one half of stock of horses, cattle, sheep and hogs and choice of ten slaves".
After John Marshall negotiated a deal and the Virginia General Assembly passed a law, the Marshall group secured temporary financing, so on August 30, 1797, Martin conveyed title to "all and every of those divers tracts, pieces and parcels of land, being part and parcel of the proprietary of the Northern Neck of Va., with all beneficial right and interest of whatsoever nature the same may be".
[44] However, the Marshall coalition did not complete their final payment until 1806, when the Northern Neck Proprietary was officially dissolved and Virginia again became legal owner of the undeveloped lands.
[11] Proprietor Adam Stephen, a close personal friend of Martin, had the town of Martinsburg in Berkeley County formally established by the Virginia General Assembly in 1778.