John Mostyn (died 1644) was a Welsh politician who sat in the House of Commons at various times between 1625 and 1640.
Mostyn was the son of Sir Roger Mostyn of Mostyn.[1] In 1624 he was elected Member of Parliament for Anglesey.[2] He was entered at Middle Temple in November 1637.
In April 1640, Mostyn was elected MP for Flintshire in the Short Parliament. He was re-elected MP for Flintshire for the Long Parliament in November 1640.[2] He was disabled from sitting in parliament for supporting the King on 5 February 1644. He was assessed at £1,000 by the Committee for the Advance of Money on 28 July 1644.[1]