He began his military career as an officer in the 9th Marines, being commissioned as a second lieutenant in 1746. But he transferred to the 10th Dragoons as a cornet in 1748, being promoted to lieutenant in 1751, captain-lieutenant in 1754 and Major in 1759. In 1760 he became a Lieutenant-Colonel in the 94th Foot, and held the same rank in the 16th Foot from 1762.
He served in both Germany and North America during the Seven Years" War, leading a division of grenadiers with great distinction at the capture of Martinique.
In 1772 he was promoted to colonel, and from 1775 until his death was Colonel of the 46th Foot. He entered the British Parliament in 1774 as member for Berwick-upon-Tweed, holding the seat for the remaining twenty years of his life.
He was appointed Governor of Fort William in 1779 and then in 1780 Governor of Berwick, also holding this post until his death, although it did not interfere with his active military career. Following the outbreak of the Vaughan returned to North America as a Major-General, serving from 1776 until 1779.
He led the grenadiers at the Battle of Long Island, and was wounded in the thigh.
He commanded a column in the Battle of Short Hills, New Jersey, in July 1777, and he commanded a column during the successful assault on Fort Clinton and Fort Montgomery, where his horse was killed under him. In 1779 he returned to England but was immediately appointed Commander-in-Chief in the Leeward Islands: he served in the West Indies from 1779 until 1782, taking a leading part in Rodney"s Capture of Street Eustatius in 1781. He was promoted to Lieutenant General in 1782.
1792 he was knighted as a Knight of the Bath (KB).
In 1795 he was appointed once more to command in the Leeward Islands, but died later the same year at Martinique.
Later in the year he was accused of embezzling the property confiscated at Street Eustatius, and was forced to defend himself against Burke"s attack in Parliament, stating that he had not profited by a shilling and had always acted in the national interest rather than his own.
14th Parliament of Great Britain. 15th Parliament of Great Britain. 16th Parliament of Great Britain.
17th Parliament of Great Britain]
From 1776 to 1783 he was also a member of the Irish Parliament and represented Street Johnstown (County Longford).
He was a reliable supporter of the government when in the House of Commons, but of course could not attend while he was absent on active service: at the 1780 election the government"s election managers considered trying to replace him temporarily as Berwick"s Member of Parliament by someone who would be able to attend and vote, but the borough"s patrons would have none of it and he was returned unopposed.