Wallace learned to play several instruments as a boy, including the violin, clarinet, organ, and piano. In 1830, at the age of 18, he became organist of the Roman Catholic Cathedral at Thurles, County Tipperary, and taught music at the Ursuline Convent there. He fell in love with a pupil, Isabella Kelly, whose father consented to their marriage in 1832 on condition that Wallace become a Roman Catholic. The couple soon moved to Dublin, where Wallace was employed as a violinist at the Theatre Royal.