 Devlin was born in Youghal, County Cork, Ireland on 10 March 1921, the only son of Richard and Mary (née Hill).His education began in 1927 at the Loreto Convent in Youghal and he later attended the Christian Brothers School in 1933.Devlin finished completed his schooling in 1939 at the Cistercian College in Dublin and concluded his ecclesiastical studies in 1945 at the Pontifical Beda College in Liverpool.