Bill (in full, William John) Mc Cormack was born in Dublin on 15 September 1947, the fourth son of Charles Elliott Mc Cormack and the only son of Irene Kathleen Mc Cormack (née King), second wife. He was educated at Rathgar National School, Wesley College, Dublin University (Trinity College), and the New University of Ulster. His father died in 1960. Between 1965 and 1967, he worked in Hodges Figgis bookshop on Dawson Street, which opened up a panorama of books, Irish and imported, new and antiquarian, and drew in numerous affable customers including Robert Barton, Eavan Boland, James Dillon, Brendan Kennelly, Mary Lavin, Frank O’Connor, Eoghan O Tuairisc, and others.
In the summer of 1967, he attended the Yeats Summer School in Sligo.