William "Billy" Holmes (2 April 1779 – 26 January 1851) was an Irish Tory and Conservative politician in the United Kingdom in the early nineteenth century. He was an MP for 28 years.

He was born in County Sligo, the son of Thomas Holmes of Farmhill, a brewer, and his wife Anne Phibbs, daughter of Harlow Phibbs. He matriculated in 1795 at Trinity College, Dublin, but did not take a degree. Then an army officer, he was secretary to Sir Thomas Hislop, 1st Baronet with rank of captain in the West Indies, from 1803 to 1807. Retiring from the army in 1807, he married and entered Parliament in 1808, as Member for Grampound.^[1]

Holmes served as party manager, and Chief Whip in the House of Commons from about 1818 until his seat (for the rotten borough of Haslemere) was abolished by the Great Reform Act of 1832. He had also previously represented several other constituencies. In the dedication to his novel The Member: An Autobiography (1832), the Scottish author John Galt pays sardonic tribute to his skillful dispensation of political patronage.^[2] After the Reform Act Holmes was out of the Commons for five years, but returned in 1837 as MP for Berwick-upon-Tweed.

Holmes was also Treasurer of the Ordnance from 1818 to 1831.

His wife was Helen Tew, Dowager Lady Stronge (1769–1852), widow of Sir James Stronge, 1st Baronet of Tynan Abbey, County Armagh, Ireland (1750–1804).

Holmes died in 1851 aged 71 and is buried in Brompton Cemetery, London.^[3]