Osborne, Sir William (1722–83), 8th baronet, politician, was eldest son among six sons and four daughters of John Osborne, MP for Lismore (1719–27) and Co. Waterford (1727–43) and 7th baronet, and his wife, Editha Proby, daughter of the governor of Fort St George in the East Indies. Educated at Jesus College, Cambridge, William succeeded as 8th baronet (11 April 1743) on the death of his father. Sheriff of Co. Waterford in 1750, he decided on a political career and was returned for the family interest as MP for Carysfort, Co. Dublin, in 1761. After representing the constituency for seven years, he then served (1768–83) as MP for Dungarvan, Co. Waterford. On 7 May 1770 he was made a privy councillor and, following a long drawn-out negotiation, decided to join the administration. He was appointed a commissioner of excise, but was dismissed by the lord lieutenant two years later for being too independent and refusing to follow the government's instructions. An excellent speaker, Osborne was unmanageable in the commons, and resolutely followed his own line of conduct. After his dismissal he made various attempts to embarrass the government but was regularly thwarted, and his reputation was damaged in 1774 when it was revealed that he had voted for the controversial stamp act. Although somewhat eccentric in his choice of issues, he was a formidable figure in the commons and was adept at leading the opposition attacks alongside Henry Flood (qv), Barry Yelverton (qv), Denis Daly (qv), and George Ogle (qv). Respected as an improving landlord, he was one of the few people praised by Arthur Young (qv) after his tour of the country. In Co. Tipperary he advanced capital for the reclamation of waste land, which was used to provide land for homeless labourers. Osborne was returned for Carysfort in August 1783 but his second period in the constituency was brief; he died in October and was buried on 27 October 1783.
He married (20 March 1749) Elizabeth Christmas of Whitfield, Co. Waterford, whose father, Thomas, was an MP; she brought with her a dowry of £5,000. They had six sons and three daughters. Four of his sons were members of the Irish house of commons, all representing the Carysfort constituency: Sir Thomas Osborne (1753–1821), MP 1776–97 and 9th baronet; John Proby Osborne (1755–87), MP 1783–7; Sir Henry Osborne (1760–1837), MP 1797–9 and 11th baronet; and Charles Osborne (1759–1817), MP 1790–1800. The third son, William, was a protestant clergyman. Osborne's second daughter, Elizabeth, married (1774) John Joshua Proby (qv), 1st earl of Carysfort.