William Selwyn was born in Caernarfon in 1933. From 1952 until 1954 he served his National Service in the Royal Artillery and then entered Bangor Normal College in 1954 staying until 1956. He subsequently taught at Maesincla Junior School and Syr Hugh Owen School until his retirement in 1990. Since retiring William Selwyn has focused solely on painting.
His art revolves around the landscape of Gwynedd, farm workers and fishermen. He is a member of the Royal Cambrian Academy. Works purchased by Gwynedd Council, Anglesey Council, University of North Wales, Bangor, The Arts Council of Wales, National Library of Wales, Bath University, and many private collections both at home and abroad.