Scully was born in Ireland, but moved with his family to England in 1949. There he studied art first in Croydon and later at Newcastle University and at Harvard University in the United States. He settled in New York City and became an American citizen in 1983.
Scully's paintings are often made up of a number of panels, and are abstract. Most of his pieces feature stripes and in some alternating areas of vertical and horizontal stripes are arranged in a chessboard pattern. Scully paints in oils, sometimes laying the paint on quite thickly to create textured surfaces.
Scully was nominated for the Turner Prize in 1989 and 1993.