James Vernon (1646–1727) was an English politician and Secretary of State for both the Northern and the Southern Departments during the reign of William III.
Vernon was a younger son of Francis Vernon of London (a scion of the Vernons of Haslington, Cheshire, and Hanbury, Staffordshire), by his wife, Anne Welby, widow, daughter of George Smithes, a London goldsmith. Like his elder brother Francis, he was an alumnus of Charterhouse and Oxford, where he matriculated from Christ Church on 19 July 1662, graduated B.A. in 1666, and proceeded M.A. in 1669. In 1676 he was incorporated at St John's College, Cambridge, which university he represented in the parliament of 1678-9.
Vernon was employed by Sir Joseph Williamson to collect news in Holland in March 1671-2, and in the following June attended Lord Halifax on his mission to Louis XIV. On his return he became secretary to the Duke of Monmouth; he it was that erased the obnoxious adjective 'natural' from the patent conferring the command-in-chief upon the duke in 1674 but left his service in 1678. He then entered the secretary of state's office as clerk and gazetteer, i.e. editor of the London Gazette. These duties he exchanged on the revolution for the post of private secretary to Lord Shrewsbury. On Shrewsbury's resignation, Vernon served in the same capacity Sir John Trenchard, by whom he was employed in Flanders in the summer of 1692 to furnish reports of the movements of the army to Sir William Dutton Colt, British minister at Celle. In 1693 he was appointed to a commissionership of prizes, which he held until 1705. On 30 October 1695 he was returned to parliament for Penryn, Cornwall, and on 22 July 1698 for Westminster, which seat he continued to hold until the dissolution of 2 July 1702. He again represented Penryn in the parliaments of 1705-7 and 1708-10. On Shrewsbury's return to power (March 1693-4) Vernon resumed in name his former relations with him. Shrewsbury's ill-health, however, and the course of events soon thrust Vernon into prominence, and during the king's absences on the continent he acted as secretary to the lords justices. On him fell the main burden of investigating the assassination plot, and of hushing up the charges brought by Sir John Fenwick (1645–1697) against Godolphin, Shrewsbury, Marlborough, and Russell. In support of the bill for Fenwick's attainder he made on 25 November 1696 the only important speech which he is recorded to have delivered throughout his parliamentary career. The dexterity which he displayed in this affair, and Shrewsbury's virtual retirement, enhanced his consequence, and at Sunderland's suggestion he received the seals on the resignation of Sir William Trumbull, and was sworn of the privy council (5 December 1697). Though he did not formally succeed to Shrewsbury's department on his resignation, 12 December 1698, he was thenceforth virtually secretary for both departments until the delivery of the southern seals to the Earl of Jersey, 14 May 1699.