 From 1945 to 1950, he was rector of All Saints Episcopal Church, in Winter Park, Florida, His last rectorship at St. Peter's Episcopal Church, in St. Petersburg, Florida began in 1950 and ended in 1961 when he was elected suffragan bishop of the Episcopal Diocese of South Florida.In 1969, he was elected the first bishop of the newly formed Episcopal Diocese of Southeast Florida and served until he retired in 1980.After retirement, Duncan remained active in the Diocese.