Alun Williams was born in Port Talbot, South Wales, the son of a Presbyterian minister. He was educated at Llandeilo Grammar School, Pontypridd Grammar School and University College, Cardiff. He then served in the Royal Navy, rising from ordinary seaman to become an intelligence officer serving in the Far East.

He began his broadcasting career when he was a student and after working as an outside broadcast assistant became a commentator for the BBC. He introduced many successful radio programmes in the 1950s including Welsh Rarebit and Workers' Playtime, and went on to present a number of long-running programmes in both English and Welsh on Radio Wales and Radio Cymru including Dewch am Dro, One Good Turn, On the Road, Monday Morning Miscellany, Alun yn Galw and Shw Mai Heno

He was a familiar face on television in Wales and for many years was one of the presenters of Come Dancing.

He was a member of the Gorsedd with the pseudonym 'Crwydryn' (Wanderer) – a reference to the extensive travelling he undertook during his career, touring with the Welsh rugby team and British Lions, presenting Forces' Chance and covering the Olympic and Commonwealth Games.

He was made an officer of the Order of the British Empire (OBE) for services to broadcasting in 1982.

He was married to Perrie Hopkin Morris, daughter of Liberal MP Sir Rhys Hopkin Morris and his wife Gwladys.