Brigadier General William Campbell (c. 1745 – August 22, 1781) was an American military officer, farmer and politician. One of the thirteen signers of the earliest statement of armed resistance to the British Crown in the Thirteen Colonies, the Fincastle Resolutions, Campbell represented relatively new Washington County in the Virginia House of Delegates. A militia officer during the American Revolutionary War, he was known to Loyalists as the "bloody tyrant of Washington County", but to the Patriots he was known for his leadership at the Battle of Kings Mountain and the Battle of Guilford Courthouse.

Born in then-vast Augusta County, Virginia to the former Margaret Buchanan and her farmer husband, Charles Campbell (d. 1767). Of Scots-Irish descent, He was baptised at Tinkling Spring Presbyterian Church on September 1, 1745. Educated by private tutors and then at Augusta Academy (a forerunner of Washington and Lee University), he became noted for his courtesy, as well as fiery temper. He had a cousin and brother in law, Arthur Campbell, who also served in the Convention of 1776.

Upon his father's death, Campbell inherited a large estate in southwestern Virginia, where he relocated his mother and sisters four years later. He established a plantation called "Aspenvale" about twenty miles from what he later helped found as Abingdon, in what a half century after his death would become Smythe County.

In his lifetime, Augusta County, Virginia was split and Botetourt County created in 1770, then Fincastle County, Virginia in 1772. Campbell was one of the justices of the peace upon the organization of Fincastle County in 1773, and the following year was a captain of one of the county's militia units. In 1775, Campbell was one of the thirteen signers of the Fincastle Resolutions, the earliest statement of armed resistance to the British Crown in the Thirteen Colonies, suggesting independence from Kingdom of Great Britain if the government failed to protect colonists from attack. Campell became captain of the first regiment of regular troops raised in Virginia, in 1775.

In 1776, Fincastle County was eliminated upon the creation of Montgomery and Washington County and Kentucky County. Campbell became a justice of the peace for Washington County, as well as one of its militia leaders. However, exposure of his family to native american attacks led him to resign his commission and return to Washington County, where he became first lieutenant colonel of the local militia, then succeeded Evan Shelby as colonel. Washington County voters elected Campbell as one of their representatives in the Virginia House of Delegates twice: in 1780, and again in 1781 (the year that he died).

As a militia leader of the American Revolutionary War, Campbell became known for harsh treatment of Loyalists. He reportedly executed at least one loyalist, and possibly a dozen, thus leading to their label of him as the "bloody tyrant of Washington County".

Promoted to colonel in 1780, he led his militia to victory at the Battle of Kings Mountain, where he charged the enemy while telling his men to "shout like hell and fight like devils!" Afterward, he worked in conjunction with Continental Army troops to oppose the British invasion of Virginia, providing support at the Battle of Guilford Courthouse. The Virginia Assembly commissioned him a brigadier general in 1781 (the same rank of General Lafayette), as well as voted him a horse, sword and pistols. However, he died campaigning in Tidewater Virginia soon afterward in the closing days of the conflict.

On April 2, 1776, Campbell traveled to Hanover County, Virginia, where he married Elizabeth Henry, sister of Virginia Governor, Patrick Henry, whom he may have met during his legislative service. They had two children: Sarah Buchanan Campbell, and Charles Henry Campbell.