Mark Fraser Williams (born 24 March 1966) is a British politician, who was the leader of the Welsh Liberal Democrats from 2016 to 2017. He is a former Member of Parliament (MP) for the Ceredigion constituency, between 2005 and 2017. He sat on the Welsh Affairs Select Committee, and in 2006 he became a Shadow Minister for Wales under Menzies Campbell. Williams is a graduate of the University of Wales, Aberystwyth and the University of Plymouth, and is now Headteacher of a school in Llangorse near Brecon.