It looks like Sir William Mansel, my 4xgreat-grand father had a career as an MP for Carmarthenshire for a short period.
I was able to find the following information thanks to the history of parliament online website:
https://www.historyofparliamentonline.org/volume/1754-1790/member/mansel-sir-william-1739-1804#family-relations
Sir William Mansel was MP for Carmarthenshire from 1784-1790.
b. 1 Mar. 1739, o.s. of Sir Richard Mansel, 8th Bt., by his 2nd w. Rebecca, da. of William Ware of Farranalough, co. Cork. m. 26 Aug. 1765, Mary, da. of John Philipps of Coedgain, sis. of George Philipps, 7s. 4da. suc. fa. Feb. 1749.
Biography
Mansel was returned unopposed for Carmarthenshire in 1784 as a follower of Pitt. His only known vote was with Administration on Richmond’s fortifications plan, 27 Feb. 1786, and there is no record of his having spoken in the House. In 1789 he began to canvass Carrnarthen borough against the next general election, and complained to Lord Hawkesbury of the little support he received from Administration:1 ‘I believe my political principles are well known, and from which I shall never depart, therefore am the more surprised I have not better support from those in power.’ Probably his absence from the divisions on the Regency did not commend him to Pitt. In the event Mansel did not stand in 1790.
He died 3 Jan. 1804.
