Willcocks returned to Cambridge in 1945 to complete his studies, and in 1947 was elected a Fellow of King's College and appointed Conductor of the Cambridge Philharmonic Society. In the same year, he became the organist at Salisbury Cathedral and the conductor of the Salisbury Musical Society. He moved to Worcester Cathedral in 1950 and remained until 1957, during which time he was organist of the cathedral, principal conductor of the Three Choirs Festival in 1951, 1954, and 1957, and conductor of the City of Birmingham Choir. From 1956 to 1974 he was also conductor of the Bradford Festival Choral Society, whilst continuing as guest conductor for their carol concerts into the early 1990s. Composers with whom he collaborated included Vaughan Williams, Britten, Howells and Tippett.