Gant attended Radley College before going on to read Music and English at St John's College, Cambridge. He was a choral scholar and sang in the College Choir under George Guest. He subsequently studied composition with Paul Patterson at the Royal Academy of Music and completed his PhD at Goldsmiths College, University of London. He is Stipendiary Lecturer in Music at St Peter's College, University of Oxford, and held the same position at St Edmund Hall until 2014.
He is an experienced singer, having sung with most of the United Kingdom's leading choirs and vocal ensembles including The Sixteen, the Monteverdi Choir and the Cambridge Singers and the Tallis Scholars. He has held posts as a church musician at Westminster Abbey, Selwyn College, Cambridge, The Royal Military Chapel (the Guards' Chapel), and Worcester College, Oxford. In September 2000 he was appointed Organist, Choirmaster and Composer at Her Majesty's Chapels Royal. He has led the Chapel Royal choir at, among many other events, the funeral of H.M. Queen Elizabeth the Queen Mother, the Golden Jubilee service in St Paul's Cathedral in 2002, the 10th anniversary service for the death of Diana, Princess of Wales, the wedding of H.R.H. Prince William and Kate Middleton in 2011, the annual Remembrance Day parade at the Cenotaph and the annual Royal Maundy service. During the Summer of 2002 he was featured in a BBC Radio 4 documentary.
Gant set the text of the Poet Laureate Andrew Motion to music, creating A Hymn for the Golden Jubilee as part of the 2002 jubilee celebrations, at the request of the Lord Chamberlain's Office at Buckingham Palace. This piece was sung at many places across the world, including at the National Cathedral of Canada, by the RSCM in Australia, and to Queen Elizabeth II in a concert at Windsor Castle. It was also featured on the official Jubilee CD produced by the Royal Philharmonic Orchestra and the Choir of St Paul's Cathedral. This recording was broadcast on BBC Radio 2, 3, and 4, and on Classic fM, where it featured high in the Classical Music Charts.
Other compositions include "The Vision of Piers Plowman", an oratorio for the 2002 Three Choirs Festival, "A British Symphony", premiered by the Philharmonia in 2007, "May we borrow your husband?" an a cappella opera, "Don't go down the Elephant after midnight", an opera for soprano Patricia Rozario, a song-cycle for counter-tenor James Bowman, and several works for choir.
2013 saw the beginning of an association with Profile Books. Gant's first title for the publisher was "Christmas Carols: from village green to church choir", published in 2014. A US edition, "The carols of Christmas", was published by Thomas Nelson in 2015. A second title for Profile, "O Sing unto the Lord: a history of English Church Music" followed in 2015, receiving favourable notices across the national media. A US edition was published by University of Chicago Press in 2017, receiving favourable reviews in, among other publications, The New York Times. His contribution to Profile's series "Ideas in Profile", called simply "Music", was published in early 2017. Gant is currently working on a book about the sources and recpetion of Handel's "Messiah" for the Bodleian Press, Oxford, and a major one-volume history of music for Profile, due for publication in 2019. Gant has appeared at literary festivals across the UK and further afield, and on national TV and radio.
In May 2014 he was elected to Oxford City Council at a by-election as Liberal Democrat councillor for the Summertown ward, also serving as chair of his party group on the council, and speaking on a range of issues. He was re-elected in May 2016 and took over as leader of the LibDem group and leader of the opposition. In July 2016 he became the Liberal Democrat prospective parliamentary candidate for the Cotswolds constituency. When the General Election was called for June 8, 2017 he was reselected as the party's candidate.