Blatty was born in New York City, the son of Lebanese parents Mary (née Mouakad) and Peter Blatty, a carpenter. His father left home when William was six years old. Raised in relative poverty by his deeply religious Catholic mother, he apparently lived at twenty-eight different addresses during his childhood. He attended several Catholic and Jesuit schools before finding his raison d'etre and attending Georgetown University and George Washington University to study English. In the mid-1950s, Blatty was a contestant on the quiz show You Bet Your Life, winning $10,000: enough money to enable him to devote more time to writing professionally.