Rielly was born in Wales and lives in London. He studied at Deeside College, Gloucester College of Art and Design and Belfast College of Art. Rielly's large paintings form a kind of perverse family album. His figures are composed of images from books and magazines, greatly enlarged. Dealing in particular with the theme of childhood and experience, Rielly's subjects include children with adult heads, identical twins, smiling children with slight deformities, pain and illness. The paintings are a mixture of the funny, the sinister and, often, the sexually provocative.