Bruce was a one-time colleague of Robert Koch in Berlin but spent the greater part of his career as a military physician. Born in Melbourne, Australia, he was educated at Edinburgh University. He was assistant professor of pathology at the Army Medical School, Netley (1889–94), and then commandant of the Royal Army Medical College, Millbank, where he was also director of research on tetanus and trench fever (1914–18). He undertook royal commissions of enquiry into various diseases of man and domestic animals in Malta and central Africa. In Malta he was able to trace the cause of Malta fever (brucellosis or undulant fever found in the milk of goats) to a bacterium later named for him as Brucella melitensis. Bruce also investigated the cause of nagana, a disease of horses and cattle in central and southern Africa, and found it to be transmitted by a trypanosome parasite carried by the tsetse fly. This work was of great help in his later research on sleeping sickness (trypanosomiasis), which he also proved to be transmitted by the tsetse fly. The recipient of many honors for his humanitarian work, Bruce was chairman of the War Office's Pathological Committee during World War I. He was knighted in 1908.