John Garnett (1707/08–1782) was an English bishop of Clogher in the Church of Ireland.
Garnett was born at Lambeth in 1707/8. His father, John Garnett, was rector of Sigglesthorne, in the East Riding of Yorkshire. His grandfather had been vicar of Kilham, and his great-grandfather a merchant in Newcastle. Educated at a school in Beverley, Yorkshire, he was admitted to St John's College, Cambridge in 1725, though he migrated to Sidney Sussex College in September 1728. Graduating B.A. in 1728/9 and M.A. in 1732, he became a fellow of Sidney Sussex in 1730, and was Lady Margaret preacher to the university from 1744 to 1752.
In 1751 Garnett went to Ireland as chaplain to the Lord Lieutenant, Lionel Sackville, 1st Duke of Dorset. In 1752 he became Bishop of Ferns and Leighlin; he was translated to Clogher in 1758, and remained bishop of Clogher until his death. In 1765 he was touted as a possible successor to William Carmichael as Archbishop of Dublin, though the Irishman Arthur Smyth was ultimately appointed.
Garnett died on 1 March 1782 at his home in Leinster Street, Dublin. There is a mural tablet to his memory in the chancel of St Lawrence's Church, Sigglesthorne, and a painting of him in St John's College, Cambridge.
Garnett married Dorothea, the youngest daughter of Sir Thomas Molyneux, 1st Baronet. According to the DNB, the John Garnett who was appointed dean of Exeter in February 1810, and died 11 March 1813, in his sixty-fifth year, was the Bishop's son.