[5][6] A friend of John Wilkes, Mullett became a leader of Bristol radicals, with Henry Cruger and Samuel Peach.
[8] Burke was willing in 1779, however, to help Mullett release James Caton, a pro-American, from the press gang, with John Dunning applying under habeas corpus.
[9] Jared Sparks conjectured that Mullett might have been the author of an unsigned letter from Bristol, to William Palfrey and containing intelligence, dated 16 February 1776.
[3][11][12] He wrote to John Wilkes about his travels, from Charleston, South Carolina, on 15 February, describing how he had started from Portsmouth, New Hampshire, and the prospects of trade, with New York impressive; noting also the remaining strong feeling against some of the British military leaders from the war.
[15][16] In February 1788 he was in Bristol, recently returned from America, and called on Sarah Fox the diarist to pass on news.
[15] Mullett moved to London around 1790, and was in business there with Joseph Jeffries Evans, his nephew by marriage, as an agent for American trade.
[21] He supplied Whitbread with figures for a major speech in parliament against the Orders in Council used to enforce the wartime blockade against the UK's enemies (as did George Joy); as well as appearing before the House of Lords on 22 February, and attending as one of the petitioners in person against them on 23 March, in 1808.
[33] Mullett had an introduction in 1783 from Samuel Stennett, a friend, to James Manning, President of the Baptist College of Rhode Island (now Brown University).
[37] After her death, Thomas Mullett and his son-in-law became Unitarians, in the Worship Street congregation of John Evans (1767–1827).