Sir James Mansfield, SL KC (originally Manfield; 10 May 1734 – 23 November 1821) was a British lawyer, judge and politician.

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.

In 1777, he was defence counsel for John the Painter, and crown prosecutor in 1779 against the counsellors who arrested Lord Pigot and took over Fort St George.

His ability was admired by the North Ministry, and he was offered a seat at Morpeth in 1776 by the Earl of Carlisle, but declined lest it interfere with his prospects for a judgeship.

Mansfield finally did enter the House of Commons in 1779 as member for Cambridge University, replacing the newly acceded Duke of Rutland.