Sumsion also led an active professional life outside the cathedral. He had begun composing as a young man and continued to accept commissions when he was well into his eighties. Possibly his last work was a set of hymns entitled 'Four Hymns', to words by Paul Wigmore, and published by Oecumuse in the autumn of 1995, only weeks after Sumsion's death. He composed many works for organ and choir, as well as chamber and orchestral pieces and a book of piano exercises. Sumsion also taught piano, organ, and composition privately, adjudicated at competitions, accompanied vocalists and played with chamber groups, and performed as an organ recitalist. His 1965 recording of Elgar's Organ Sonata, which he recorded in one 'take', is now regarded as the standard interpretation of that work. Concurrent with his post at the cathedral Sumsion served as director of music at Cheltenham Ladies' College (1935–1968) and directed the Gloucester Choral and Orchestral Societies. As a teacher and choir trainer he was said to be demanding yet kind and encouraging, displaying 'that rare gift that made people want to do well for him'. Sumsion was honored with a Lambeth Doctorate in 1947 and was appointed CBE in 1961.