Williams was born in Llangefni, Anglesey into an old landed Anglesey family. His father was a bank manager. Kyffin Williams was educated at Moreton Hall School then Shrewsbury School before joining the 6th Battalion Royal Welch Fusiliers as a lieutenant in 1937. After he failed a British Army medical examination in 1941 (because of epilepsy), his doctor advised him to take up art for the sake of his health. His works typically drew inspiration from the Welsh landscape and farmlands. His works may be seen in a permanent exhibition at Oriel Ynys Môn, Anglesey, as well as at many other galleries elsewhere in Britain. He was President of the Royal Cambrian Academy and was appointed a member of the Royal Academy in 1974. In 1995 Williams received the Glyndŵr Award for an Outstanding Contribution to the Arts in Wales during the Machynlleth Festival. He was awarded the OBE for his services to the arts in 1982 and a KBE in 1999.