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.2See C11/703/15, N. Barnardiston v. W. Codrington, 21 Jan. 1723. He returned to England c.1730, and set up as a London merchant. Some information about his trade appears in the evidence he gave before the House of Commons on 16 Feb. 1736: he was sending ‘great quantities’ of English woollens to the Guinea coast, purchasing there negroes for the British plantations, and receiving in exchange ‘the produce of the said islands, and particularly cotton’.3CJ, xxii. 566.
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.4V. L. Oliver, Antigua. 43.