John Leslie (14 October 1571 – 8 September 1671) was a combative Scottish royalist bishop of Clogher, who became known as the "fighting bishop" for his resistance to the Irish rebellion of 1641 and the parliamentarian forces.
The oldest son of George Leslie and Marjory, his wife, he was born at Crichie in Aberdeenshire, 14 October 1571. He was educated at Aberdeen and afterwards in France. He lived abroad for two decades, mainly in Spain, where his Latinity was admired. He was admitted to read in the Bodleian Library in 1618, and in 1624 he graduated Doctor of Divinity (DD) at Trinity College, Cambridge, per literas regias. He was in favour with James I, who made him a privy councillor in Scotland, and with Charles I, who gave him the same rank in Ireland, and this he retained after the Restoration. He was with George Villiers, 1st Duke of Buckingham at Rhé in 1627.
His first preferment seems to have been in London to the church of St. Martins-in-the-Vintry, and he was promoted to be Bishop of the Isles in 1628. In June 1633 he was translated to the bishopric of Raphoe in Ireland. Here he found many of the mensal lands in the hands of lay usurpers, but recovered some by a lawsuit to i. In 1635 he had a dispute with one John Hamilton, in which John Bramhall, at Thomas Wentworth's request, undertook to arbitrate. He built a fortified palace at Raphoe, where there had been no episcopal mansion.
The outbreak of the Irish rebellion in 1641 tested the defences of the palace. The bishop raised a company of foot for the king, distinguished himself as a partisan leader, and conveyed ammunition through from Dublin to Derry. He relieved Sir Ralph Gore, who was hard beset at Magherabeg, near Donegal. Leslie is said to have gone to Scotland about midsummer 1642, all the other bishops having previously left Ireland; but he returned after the king's execution, defended Raphoe against the Cromwellians as he had done against the Irish, and was one of the last royalists to submit.