 He was made a deacon in 1977, ordained to the priesthood in 1978, and served a number of parishes in the Diocese of Toronto before becoming executive assistant to the diocesan bishop in 1992 and archdeacon of York in 1994.Johnson was elected suffragan bishop by the diocesan synod on April 23, 2003, at the Cathedral Church of St. James (Toronto) and was consecrated on June 21, 2003, to serve as the area bishop of Trent-Durham, the eastern region of the diocese.He was elected diocesan bishop on June 12, 2004, and installed as the 11th bishop of Toronto on September 12, 2004.