He was born in Salford and attended Salford Grammar School, his father was a jazz musician and his mother was a school teacher. He sold his first painting at the age of eleven to the City Art Gallery. At the age of seventeen he won a scholarship to The Slade and went on to study in Italy and Spain before returning to the City of Salford where he has lived ever since. As a student he became a close friend of L. S. Lowry and together they worked on a project to record the area and it's people. Riley continued this work long after Lowry's death.
As well as this body of work, he developed a reputation as a portrait painter. He has painted many famous people including Nelson Mandela and Pope Paul II.
His sporting works, particularly those of golf and football are also very sought after.
He has been awarded honorary doctorates by the University's of Salford, London, Florence and Manchester.
Salford City Council have funded an archive and studio for Riley in the conservation area around the old Salford Fire Station, where he continues to work.