Alexander Gillies was born in Ravensbourne, Dunedin, on 26 September 1891, the son of Scottish parents Gilbert Wilson Gillies, a boilermaker, and his wife, Agnes Gibson. He attended Otago Boys’ High School and went on to the University of Otago, where he gained a rugby blue. From 1916 until early 1919 Gillies served with the New Zealand Expeditionary Force in the Middle East. An NZEF scholarship enabled him to study medicine at the University of Edinburgh from 1919 and he graduated MB, ChB in 1923. He gained his FRCSE in 1926. On 21 September 1920, in Glasgow, he married Canadian-born Effie Lovica Wooler (née Shaw).
Gillies was diverted from a planned career in public health to work with Sir Robert Jones, the founder of British orthopaedics, at the Shropshire Orthopaedic Hospital, Oswestry, and at the Royal Southern Hospital, Liverpool. During this period he acquired a Liverpool diploma in radiology. He worked at the Mayo Clinic in Rochester, Minnesota, in 1927 and at the Lockwood Clinic, Toronto, in 1928–29 before returning to New Zealand to practise in Wellington and take up an appointment as orthopaedic surgeon to Wellington Hospital.
In 1932 Gillies became a fellow of the recently established Royal Australasian College of Surgeons, on whose court of examiners he later served. On a return visit to Liverpool in 1936 he gained the master of orthopaedic surgery degree. His service in Wellington was punctuated not only by that visit, but by two years in London during 1940–41 as resident commissioner of the British Red Cross Society and Order of St John of Jerusalem. He retired from his hospital appointment in 1950, but remained in private practice with satellite hospital appointments in Nelson and Dannevirke for some years.
Gillies was chairman and later president (1953–61) of the New Zealand Red Cross Society. In 1935 he and his friend and fellow Rotarian Charles Norwood were instrumental in establishing the New Zealand Crippled Children Society, and he was president in 1966. Among the other organisations he helped found were the New Zealand Association of Health, Physical Education and Recreation, and, in 1950, the New Zealand Orthopaedic Association, of which he was the first president for a two-year term. His widespread interest in physical therapy was reflected in his long-term membership of the Physiotherapy Board. In 1959 he was made knight bachelor.
Although Gillies achieved considerable success in his career, his family life had elements of tragedy: one daughter died in adolescence; he suffered his first stroke in 1966; and Effie died in 1972 and his other daughter in 1977. Gillies seemed to be facing the prospect of a lonely old age, deprived of playing golf, a sport he particularly loved. However, on 25 July 1978, in Wellington, he married Joan Mary Kennedy, an executive secretary, who was the daughter of his old friend Francis Kennedy. She was indefatigable in enabling him to attend events connected with his favourite organisations, and he derived special pleasure in 1980 from his involvement in the 30th jubilee of the New Zealand Orthopaedic Association, held at the Chateau Tongariro.
Alexander Gillies died in Wellington on 19 February 1982, survived by his second wife; his funeral in St John’s Presbyterian Church, which he had served as an elder for many years, was an occasion of some grandeur. His colleagues were wary of him, but he was a prominent figure in the establishment of orthopaedic surgery as a specialty in New Zealand, and his commitment to good causes had earned him great repute in the community.