 On 7 January 2012, Mercer was received into the Roman Catholic Church as a member of the Personal Ordinariate of Our Lady of Walsingham at St Agatha's Church, Landport.On 27 March 2012, he was ordained a Catholic priest by Bishop Alan Hopes in the Cathedral of St John the Evangelist, Portsmouth.On 21 June 2012 it was announced that he had been elevated to the rank of Chaplain of His Holiness, entitling him to the title of monsignor.