Innes Wares Brebner matriculated in 1898 and the next year passed the intermediate examination for the BA degree (equivalent to the first year of study) of the University of the Cape of Good Hope. Proceeding to Scotland he qualified as Bachelor of Medicine and Bachelor of Surgery (MB, ChB) at the University of Edinburgh in 1906. Upon his return to South Africa he was licensed to practice in the Cape Colony in December 1906 and was appointed as medical officer at Grey Hospital in King William's Town. In 1907 he obtained an appointment as resident house surgeon at the Johannesburg Hospital and was licensed to practice in the Transvaal Colony the next year. However, in 1911 he set up private practise in Turffontein, Johannesburg. In 1915 he was appointed to the honorary staff of the Johannesburg Hospital as a surgeon. During World War I (1914-1918) he served as a captain in the Medical Corps in France and was subsequently honoured as a Member of the Order of the British Empire (MBE).
After the war, in April 1922, Brebner was reappointed to the staff of the hospital as senior honorary visitinbg surgeon. In 1923 he joined the staff of the Department of Surgery at the Medical School of the University of the Witwatersrand, under Professor G.R. Thomson*, on a part-time basis, while also maintaining his private practice in Turffontein. Two years later he went to Scotland again and qualified as a Fellow of the Royal College of Surgeons of Edinburgh. On 1 January 1931 he succeeded G.R. Thomson as (part-time) professor of surgery and head of the department. Following his promotion he soon felt that the university did not give him the support required to develop his department to an adequate standard and consequently resigned his professorship as a matter of principle. Despite these problems he remained head of the department until his retirement in 1945.
Brebner was a big man with a powerful presence who was very kind to students and was revered as a teacher. He had a formidable reputation as a surgeon, with a practical approach, but was little interested in theory and research. His special interest was in chest surgery and in 1938 he performed the first pneumonectomy [surgical removal of a lobe of the lung] in South Africa.
Brebner published several papers during his career. As co-author with Dr G.A. Turner* he produced a paper on "The serum treatment of cerebrospinal meningitis" (Medical Journal of South Africa, July 1915, pp. 205-225) in which they recommended a treatment developed in the United States. Later he described a "Case of gonococcal endocarditis" (Journal of the Medical Association of South Africa, 1927), and discussed "The case-incidence of thromboangiitis as seen in Johannesburg; diagnosis and treatment" (Ibid, 1928). After his retirement he wrote a paper on "Surgery in the Bantu" (The Leech, 1950). In 1949 he was appointed chairman of a commission of enquiry into medical training and set out their findings in his Report of the Commission of Enquiry into the Facilities of Hospitals for Medical and Dental Training (Department of Education, Arts and Science, 1950).
Brebner was elected an honorary Fellow of the American College of Surgeons in 1938, an honorary Fellow of the Royal College of Surgeons (of England) in 1945, and an honorary Fellow of the College of Medicine of South Africa in 1961. The University of the Witwatersrand awarded him an honorary Doctor of Medicine degree in 1966. In 1973 he donated the Brebner Gold Medal to the College of Medicine of South Africa for excellence in the Fellowship examinations in surgery. He was married to Irene Elizabeth Brebner, born Mabille, who died in 1961.