John Main was born in London as Douglas Main, the fourth of six children of David and Eileen Main. In the 1940s he joined the Canons Regular of the Lateran and studied at the diocesan seminary of St Edmund's College, Ware in England before being chosen to pursue theology studies at the Pontifical Athenaeum Angelicum, Rome. He began to doubt his vocation to the priesthood and decided to leave his order to go to Dublin (where his family then lived), where he studied law at Trinity College. He graduated in 1954 and joined the British Colonial Service, working as a civil servant.