On 8 May 2017, it was announced that Brewster had been made a residentiary canon of St Paul's Cathedral.[6] He was installed as a residentiary canon and appointed canon treasurer by Pete Broadbent, acting Bishop of London, during a service at St Paul's Cathedral in July 2017.[7] As Canon Treasurer he had oversight of the building and the commercial and financial aspects of the cathedral's ministry.[5]
On 13 September 2021, he was appointed interim mission community leader and transitional vicar in the Cartmel Peninsula Team Ministry in the Diocese of Carlisle; he took up the post in October 2021.[2] On 28 June 2023, he was announced as the next Dean of Carlisle, in succession to Mark Boyling.[3][8] He was installed as the 42nd Dean of Carlisle during a service at Carlisle Cathedral on 30 September 2023.[5][9]