Hemming entered the Colonial Office through competitive examination in
1860. He was promoted to clerk 3rd class in
1864 and served as private secretary to permanent undersecretary
Sir Frederic Rogers until
1871. In
1879 he became principal clerk and was in charge of the African and Mediterranean department
until
1895. He then served as Governor of
British Guyana for two years and Governor of
Jamaica until
1904. He received the KCMG in
1890 and GCMG in
1900.