The Trevanions took their name from a property in the parish of St. Michael Caerhayes, which they owned from at least the fourteenth century. Richard Trevanion, a Cornish knight of the shire in 1407, established the manor of Caerhayes as his principal seat, and his descendants, by dint of loyal service to the Tudors and astute support for the Reformation, emerged by the late sixteenth century as one of the county’s leading families. Their social connections extended well beyond the Cornish gentry, however. Trevanion’s great-aunt married Queen Elizabeth’s cousin, the 1st Lord Hunsdon (Henry Carey†), while his aunt, who wed Hunsdon’s son Sir Robert Carey*, was a Lady of the privy chamber to Anne of Denmark.
Trevanion became a Cornish magistrate in 1617, and remained prominent in local government for nearly three decades. His estates afforded him a measure of electoral patronage over several local boroughs. In 1620 Tregony provided a seat for his wife’s kinsman Thomas Malet, and at Grampound he presumably backed the duchy of Cornwall’s nominee, his uncle Sir Robert Carey. Surprisingly he was unable to secure a burgess-ship at Grampound in 1624 for his cousin Thomas Carey, who had also been nominated by the duchy, but he seems to have enjoyed greater success elsewhere in placing his friends. This claim requires some explanation. By the late 1620s Trevanion was a member of the Cornish gentry faction which formed around William Coryton*, vice-warden of the Cornish stannaries, and local political agent of the 3rd earl of Pembroke. His role within this group is difficult to document before 1628, but it is striking that from the middle of the decade the boroughs where he possessed leverage frequently elected allies of Coryton and Pembroke. In 1624, Ambrose Manaton and John Arundell were returned at Tregony and St. Mawes respectively. In the following year Sir James Fullerton, a Pembroke client, secured a place at St. Mawes, while Trevanion’s cousin, Sir Henry Carey II, sat for Tregony. Trevanion himself served as a Cornish knight of the shire in 1625, and although the evidence is not conclusive, he apparently stood in conjunction with Arundell. He left no trace on the records of either parliamentary sitting.
Trevanion’s electoral patronage continued along the same lines in 1626. He presented seats at St. Mawes and Tregony to his cousins Sir Henry and Thomas Carey, while Grampound took Sir Benjamin Rudyard and Francis Courtney, both of whom were probably members of the Pembroke-Coryton circle. William Carr, who secured the second burgess-ship at St. Mawes, was possibly also a Pembroke client. In the aftermath of this Parliament the duke of Buckingham forced the earl to strip Coryton of his local offices, and Trevanion may also have been displaced as a deputy lieutenant, as his signature disappears from militia-related documents from mid 1626.
Trevanion refused to settle his knighthood composition fine of £200 until July 1633, and it is conceivable that the burden of the shrievalty was imposed on him later that year as a punishment. He also ignored the government’s request in 1639 for a contribution towards the costs of the First Bishops’ War. Nevertheless, his attitude had softened by the following year, when he helped to impress men and organize equipment for the second war.