 Mansfield pursued a career in law, obtaining admission to the Middle Temple on 11 February 1755 and being called to the bar on 28 November 1758.His career, both at common law and in chancery, was quite successful, and he was appointed one of the counsel for John Wilkes in 1768.Mansfield was one of James Somersett's lawyers; Somersett was a slave brought by his master from Jamaica to London in 1769, and freed on 22 June 1772 by a ruling from Lord Mansfield (no relation).