Trelawny entered the army in 1672, receiving a commission in the Royal English Regiment of Foot, raised by the Duke of Monmouth, which served in the French Army in the Third Anglo-Dutch War. He was present at the invasion of the Dutch Republic and the Siege of Maastricht (1673), transferring as captain into the second battalion of the regiment, under Bevil Skelton, on 16 March 1674. He probably fought at Enzheim that year, and was at Altenheim the next, returning to England in 1677.
Trelawny was commissioned captain-lieutenant of the Duke of Monmouth's Regiment of Foot in 1678 and was promoted major on 1 November 1677. On 13 July 1680, he was appointed major of the Earl of Plymouth's Regiment of Foot, raised as part of the Tangier Garrison. (Trelawny's eldest brother, John, a captain, was killed at Tangier in May of that year.) He was promoted to lieutenant-colonel of the regiment on 27 November 1680, succeeding Percy Kirke, and succeeded Kirke as colonel on 23 April 1682. He returned to England upon the evacuation of Tangier in 1684, where part of the regiment fought at Sedgemoor the following year. Trelawny was also returned to the House of Commons that year, as Tory Member of Parliament for East Looe, a seat he retained until 1699.
One of the army conspirators against James II, Trelawny, with his lieutenant-colonel Charles Churchill, and part of his officers and men, deserted to William of Orange in November 1688 from Warminster. Dismissed by James, he was re-appointed by William on 31 December 1688 and the regiment renamed The Queen Consort's Regiment of Foot. Trelawney was promoted brigadier-general on 6 March 1689, and led a brigade in Ireland, crossing at Slanebridge to attack the Jacobite left wing at the Battle of the Boyne in 1690. He served under Marlborough that September during his campaigns, and was promoted major-general on 2 December 1690. However, he resigned the command of his regiment (which went to his brother Henry) in 1692 to protest William's preferential treatment of foreign officers.
By this time, Trelawny had obtained an estate at Hengar by marriage (1 May 1690) to the heiress and widow Anne Morice (d. 1691). He was considered for appointment as colonel of the Coldstream Guards in 1694, but was thought too obnoxious to Whig sensibilities; it went instead to John Cutts. He was made Governor of Plymouth in 1696, and was returned as member for Plymouth in 1698, holding the seat until 1713. He married again on 25 June 1699, to Elizabeth Mitchell, by whom he had one daughter. Trelawny left the governorship of Plymouth in 1722 and died at Hengar on 24 September 1731.
- Childs, John (2004). "Trelawney , Charles (1653–1731)". Oxford Dictionary of National Biography. Oxford University Press. Retrieved 2 August 2007.
- Leigh Rayment's Historical List of MPs [self-published source][better source needed]