He became Assistant and then in 1961 Master of Music at Westminster Cathedral. Whilst there he conducted the first performance of the early music vocal ensemble Pro Cantione Antiqua. He also collaborated with the London Mozart Players, the Wren Orchestra, the Belgian Radio Choir and the BBC Singers. He performed for the Queen of England at St Paul's Cathedral, for President John F. Kennedy at Westminster Cathedral, and at St. Peter's Basilica for Pope John Paul II. In 1976 he moved to Dublin where he became choral director at Radio Telefís Éireann in 1981. He founded the RTÉ Philharmonic Choir and the RTÉ children's choir in 1985. He also founded the RTÉ Chamber Choir. Mawby retired to East Anglia in 2001 but returned to County Dublin in Ireland briefly, moved to London, then Dublin again before returning to London. In 2006, Mawby was awarded by Pope Benedict XVI the Knighthood of the Order of St. Gregory, "in gratitude for past and continuing services to church music".
Works
Mawby's music for the English Catholic liturgy is prolific. He composed several masses, motets, antiphons and hymn settings. His Ave verum corpus for choir and a setting of Psalm 23 won fame in the recording by Charlotte Church. His Requiem of Hope for soprano, mixed choir and organ, composed from 1995 to 2002, is based on texts by Henry Vaughan, John Henry Newman and anonymous texts. In 2002, his Prayer of Forgiveness was awarded "Top Honors" in the competition "Waging Peace Through Singing" in Oregon, USA. A Te Deum for soprano solo, chorus, organ and brass ensemble was premiered in Cambridge in 2006 to mark his 70th birthday. His setting of Laudate Pueri Dominum was premiered in 2011 at Westminster Cathedral Hall. after the first performance of the Bonifatius Messe with choir and children's choir of St. Bonifatius, Wiesbaden in 2012 His secular works include two operas for young people, The Torc of Gold and The Quest, both on a libretto by playwright Maeve Ingoldsby, commissioned by the National Chamber Choir and premiered in Dublin under his direction. On a commission by St. Bonifatius, Wiesbaden, he composed in 2011 the Missa solemnisBonifatius-Messe for soprano, choir, children's choir, oboe and organ, premiered in his presence on 3 October 2012 to celebrate the 150th anniversary of the Chor von St. Bonifatius, with the choir and children's choir conducted by Gabriel Dessauer. Mawby commented on his writing for choirs in 2006: "I cannot write choral music unless I work with choirs. Now that's a subjective judgement: I know that lots of people can do these things; I can’t. I have to write for particular people." His works are published internationally, in Germany by Dr. J. Butz, and in Italy by Eurarte and Casa Musicale Carrara. Colin Mawby died on 24 November 2019.