Sir Kyffin Williams was educated at Shrewsbury School and worked as a land agent in Pwllheli from 1936 to 1939. He suffered from epilepsy and was encouraged to take up a ‘quiet, undemanding’ activity of painting by his doctor. He studied under Schwabe and Allan Gwynne-Jones at the Slade School of Fine Art from 1941 to 1944, which had relocated to Oxford during its wartime evacuation from London. From 1944 to 1973 he was senior art master at Highgate School in London. Williams served as president of the Royal College of Art from 1969 to 1976. He received the OBE in 1982 and was made Deputy Lieutenant for the county of Gwynedd in 1985. He was knighted in 1999.

Williams is above all remembered for his paintings of Welsh landscapes and cottages, such as Ysgoldy, Cwm Pennant (1962) and Gwastadnant (1971). Using a palette knife and thick impasto paint applied in blocks of strong colours and contrasting sombre tones, he succeeded in capturing the often turbulent weather on the rugged Welsh landscape. Williams was also a noted portraitist. In 1963 he received a Winston Churchill Fellowship to record the life of the Welsh in Patagonia, an experience which he relates in his autobiography A Wider Sky. He lived in Pwllfanogl, Llanfairpwyll and Gwynedd and retired to Anglesey in 1973.

Williams was President of the Royal Cambrian Academy from 1969 to 1976 and again from 1992. He was awarded an honorary MA from University of Wales in 1973. He was a member of the Royal Academy and the Royal Society of British Artists.