Vernon’s father, in the course of a varied but apparently successful career, acquired the rank of captain, probably at sea. He was a naval victualler in 1628 and secretary to Lord Hamilton during his campaign in (Germany. On 1 Sept. 1642 he was appointed deputy to Sir Gilbert Gerard as parliamentary treasurer at war, and held office at least until 1645. Vernon’s brother inherited an independent income, but acted as secretary to Ralph Montagu at Paris, until he retired to satisfy a taste for more extensive travelling; but before doing so he procured for Vernon a recommendation to Montagu’s successor, the 2nd Earl of Sunderland, to whose friendship, according to his son, he ‘owed the rise of all his good fortune in life’. But it was Joseph Williamson who sent Vernon on a mission to the Continent in 1672. On his return he was appointed private secretary to the young Duke of Monmouth, for whom a household had just been formed, and granted a pension of £300, in addition to which his brother’s death left him master of sufficient private means to patronize Kneller on his arrival in England, and to introduce him to court circles. When the King appointed Monmouth captain-general, Vernon is said to have razed from the commission the adjective in the phrase ‘natural son’. As field deputy to the secretary at war he must be credited with the logistical success of the expedition to Flanders in 1678. He owed his seat in the first Exclusion Parliament to his employer’s interest as chancellor of Cambridge University. Shaftesbury marked him ‘base’, no doubt because of his court connexions. He was appointed to the committee of elections and privileges, spoke twice in the debate on disbandment on 29 Mar. 1679 to deny that the army had taken free quarter or transgressed the Petition of Right, and voted for the exclusion bill.
Vernon accompanied Monmouth on his campaign against the Scottish Covenanters, but was not re-elected. His employer had renounced his interest at Cambridge, and he was twice unsuccessful at Penryn. His pension was paid up to midsummer 1680, but he continued in the same service till Monmouth went into exile, though by July 1681 he was expressing the wish that the Duke ‘would leave his party and return to the King’. A warrant was issued for his arrest during the rebellion in 1685; but in 1688 he became a Whig collaborator and was employed in the production of the London Gazette. On 27 Dec. he entered the service of William of Orange, who at first distrusted him, but soon formed a better opinion of him. He became undersecretary of state to Lord Shrewsbury, and advanced £1,500 to the new regime. At Sunderland’s suggestion he was made secretary of state in 1697. He remained a Whig, losing office at the accession of Anne and his sinecure at the Exchequer on the formation of the Tory ministry in 1710. He died on 31 Jan. 1727 and was buried with his wife at Watford. Both his sons sat in Parliament; the elder was also a government official, while the younger, the well-known admiral, sat for Penryn from 1722 to 1734 and later for other constituiencies.