Robert William Jackson entered the British Army Medical Department in 1854 and served in the Crimean War (1854-1856), India (1857-1858), and the Ashanti War (in present Ghana, 1874). He was honoured as a Companion of the Order of the Bath (CB) in 1874. In 1879 he was sent to Natal to serve in the British war against the Zulus. After the war, during October to December 1879, he accompanied the Transvaal Field Forces on their campaign against the Bapedi under paramount chief Sekhukhuni. Upon his return he and Robert Moore* published a pamphlet, Observations of cases of horse-sickness (Pretoria, 1880), dealing with cases that had occurred during the campaign. The pamphlet is thought to be the first professional veterinary publication of the Transvaal. It was also published as Government Notice 243 of 1880 in the Natal Government Gazette of 15 June 1880. Jackson also published a paper on "Enteric fever and its modifications by malaria in south-east Africa" in the Dublin Journal of Medical Science (1881), based on his experiences in South Africa.
After his departure from South Africa Jackson was stationed at the Royal Infirmary in Dublin, Ireland, but in 1882 served in Egypt. That same year he was declared a knight (Kt; that is, awarded the non-hereditary title Sir) and promoted to Deputy Surgeon-General. He later settled in Dublin.