William Conyngham Plunket, 1st Baron Plunket (July 1, 1764) - (January 5, 1854) was an Irish politician and lawyer who eventually became Lord Chancellor of Ireland. The son of a Presbyterian minister, he was born in Enniskillen, County Fermanagh, and educated at Trinity College Dublin. After graduating in 1784, he was admitted as a student at Lincoln's Inn, and was called to the Irish bar three years later. He was made a King's Counsel in 1795, and three years later was elected to the Irish House of Commons as a Member of Parliament for Charlemont.

After the Act of Union was passed, Plunket lost his seat, but he subsequently became Solicitor General for Ireland in 1803, a post he held for two years before becoming the country's Attorney General, again for two years. In January 1807, he was returned to Westminster as a Whig member for Midhurst, representing the constituency for only three months, although he subsequently returned to the House of Commons in 1812 as a member for Dublin University. Between 1822 and 1827, he was again Attorney General for Ireland, and in the latter year he became the island's Chief Justice of the Common Pleas.

In 1827, Plunket was ennobled in the Peerage of the United Kingdom as Baron Plunket, of Newton in County Cork. He was an advocate of Catholic Emancipation, and served as Lord Chancellor of Ireland from 1830 to 1841, with a brief interval when the Tories were in power between 1834 and 1835. He was forced into retirement to allow Sir John Campbell to assume office, and died at the age of 89 at his home in County Wicklow.