Jeunesse ouvrière chrétienne
Sheehan was born in Ballarat to farmer Cornelius Joseph Sheehan and Kathleen Veronica O'Donohue. He attended local Catholic schools and became a motor trades instructor, with a Trained Trade Instructors Certificate and Diploma of Technical Education from Hawthorn State College. From 1964 to 1966 he was national president of Young Christian Workers; in 1967 he joined the Labor Party. In 1982 he was elected to the Victorian Legislative Assembly as the member for Ballarat South. He served until 1992, when his seat was abolished and he was defeated in Ballarat East.