William Selwyn was born in Caernarfon in 1933. After completing National Service in the Royal Artillery, he studied at Bangor Normal College between 1954 and 1956. He subsequently taught Art at Maesincla Junior School and at Ysgol Syr Hugh Owen. Since his retirement from teaching in 1990 he has devoted himself to painting full time, becoming particularly noted for his watercolours and mixed media works.
His art is centred on the landscape and coastline of Gwynedd, its farm workers and fishermen. In 1976 he was elected to the Royal Cambrian Academy. He is the winner of a number of art prizes: the 1998 Singer & Friedlander/Sunday Times Watercolour Competition; the 2001 Welsh Artist of the Year; and the 2003 Spirit of Llyn Art Competition.