He was educated at Westminster School from 1768 to 1773 and then obtained an ensign's commission in the Coldstream Guards, in which his father was captain.
Although this bequest made him a rich man, his miserly behavior only worsened (perhaps stimulated by the example of his brother-in-law, Sir Christopher Hawkins), and there was considerable friction in his family life.
[1][3] In October 1812, Hawkins set him to contest Grampound, but he stood third at the poll, behind a coalition of Andrew Cochrane-Johnstone and John Teed.
[1] John Bruce retired in 1814 to head the Stationery Office in Edinburgh, and Trelawny-Brereton was again put in temporarily at Mitchell on 2 August.
He took the Manor of East Hendred on 5 December 1814 to make way for Lord Binning, a government candidate.