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.