He was the son of Major J Aitchison HEICS. He obtained his doctorate in medicine at Edinburgh University in 1858, and then entered the Bengal Medical Service. He harvested plants in India from 1861 to 1872, in Afghanistan from 1879 to 1885 and occasionally in Ireland 1867-1869. He published a catalog of plants of Punjab and Sindh in 1869, "On the flora of Kuram Valley, etc.. Afghanistan" in the Journal of the Linnean Society in 1880-1881 and various other publications in the publications of the Linnean Society of London (he was a member from 1863). He became a member of the Royal Society in 1883.  His herbarium is preserved in the Royal Botanic Gardens, Kew, and Calcutta.