 Johnson succeeded Caleb Lawrence of the Diocese of Moosonee, who had been the metropolitan since 2004.When the 9th Bishop of Moosonee, Tom Corston, retired on December 31, 2013, the Diocese of Moosonee was reorganized as a mission area of the Province of Ontario, with Johnson, as metropolitan, serving as bishop of Moosonee in addition to his jurisdiction in the Diocese of Toronto.He was formally installed as the 10th Bishop of Moosonee on April 1, 2014 at Bishop Anderson Memorial Church, Cochrane and enthroned at St. Matthew's Cathedral, Timmins the next day.