Bethell as a young man went out to the West Indies, and c. 1720 was ‘chief agent and manager’ of all the Antigua plantations of his brother-in-law, Sir William Codrington.
In 1754 Bethell stood for London on a joint interest with William Beckford, and came out second on the poll, receiving only six votes less than Sir John Barnard. He was classed in Dupplin’s lists as an Opposition Whig.
Bethell died 1 Nov. 1758, leaving most of his fortune, including his real estate in Antigua, to his Codrington nephews.
