Trevanion was a Member of Parliament, representing the Cornish boroughs of Grampound in the Short Parliament in 1640 and Lostwithiel in the Long Parliament from 1640 until his death in action  at the siege of Bristol.
They did not all fall at the same time, nor in the same place, but all four were killed in the year 1643. Slanning and Trevanion were slain at the siege of Bristol; Sir Bevil Grenville fell at the Battle of Lansdowne near Bath, where an obelisk has been erected to his memory; and Sir Sidney Godolphin was shot in the porch of the Globe lnn at Chagford in Devon.
Trevanion married Mary Arundell, youngest daughter of Royalist John Arundell of Trerice, and sister of Richard Arundell, 1st Baron Arundell of Trerice and had a son Charles, who was successor to his grandfather.
- John Burke A genealogical and heraldic history of the commoners of Great Britain
- Brunton, D. & Pennington, D. H. (1954) Members of the Long Parliament. London: George Allen & Unwin; p. 144
- The Gentleman's Magazine July-December 1860