Harold Delf Gillies was born at Dunedin, New Zealand, on 17 June 1882, the son of Robert Gillies, a surveyor, and his wife, Emily Street, a niece of Edward Lear, the nonsense writer and landscape painter. Robert Gillies was a member of the House of Representatives in 1884 and 1885. He died in 1886, two days before Harold's fourth birthday. Harold Gillies attended Wanganui Collegiate School between 1895 and 1900. He was a school prefect and played cricket for the First XI. On leaving school he studied medicine at Gonville and Caius College, Cambridge University, and won university blues for rowing and golf. He later played golf for England. After clinical training at St Bartholomew's Hospital, London, Gillies qualified in 1908. He became an FRCS in 1910 and specialised in ear, nose and throat surgery.
On 9 November 1911 Gillies married Kathleen Margaret Jackson, at London. During the First World War he served with the Royal Army Medical Corps, and in France was influenced by Hippolyte Morestin, a brilliant French surgeon treating injuries of the face and jaw. Gillies successfully urged upon the army authorities the need for special care in this field and a unit was set up in England under his command. By the end of the war some 11,000 patients had passed through his hands. He was made a CBE in 1920.
Gillies applied the lessons learned in war to civilian casualties and extended the techniques of plastic and reconstructive surgery. His first book, Plastic surgery of the face, was published in 1920. In hospital and Harley Street practice, and as consultant to the armed forces, he created almost single-handedly the specialty of plastic surgery. He combined technical skill with an imaginative and ingenious mind, unhindered by preconceived ideas. One of his innovations was the multidisciplinary team; for example, when operating on a face he ensured that a dental surgeon was on hand. And, because surgery on damaged faces was impossible when a mask was used to anaesthetise the patient, he encouraged anaesthetists to develop alternative techniques, such as using a tube in the trachea.
In 1923 Gillies was decorated by the Danish government for treating numerous casualties after an explosion on a Royal Danish Navy ship. He was knighted in 1930. In the 1930s Gillies was joined by two New Zealand surgeons who trained under him: Archibald McIndoe, a relative, and Rainsford Mowlem. On the outbreak of the Second World War three multidisciplinary teams were established, headed by Gillies, McIndoe and Mowlem. The teams, modelled on those Gillies had pioneered, provided plastic surgery for the armed forces. Surgeons, dental surgeons and dental technicians from round the world trained under him. The New Zealanders included W. M. Manchester, F. L. Hutter and J. J. Brownlee. These men returned home and established the specialty of plastic surgery in New Zealand. The first civilian plastic surgery unit was set up in 1945 by Manchester at Burwood Hospital, Christchurch.
In 1946 Gillies was elected foundation president of the British Association of Plastic Surgeons; he later became honorary president of the International Society of Plastic Surgeons. He was decorated by the Norwegian government in 1948 for his work during the war, and was an honorary fellow of the Royal Australasian College of Surgeons, of the American College of Surgeons and of the Royal Society of Medicine, London.
Although he treated the rich and famous for both necessary and cosmetic surgery, Gillies willingly accepted all patients who needed his skills. He was also involved in the early work on sex-change operations. In 1957 he co-authored, with Ralph Millard, the authoritative textbook The principles and art of plastic surgery. Gillies's wife, Kathleen, died on 14 May 1957 at Oakley, Hampshire. He then married Marjorie Ethel Clayton, who had been his surgical assistant for many years, on 5 November 1957, in London. Outside his professional life Gillies was an artist: he exhibited his work in London on two occasions and another exhibition was held posthumously in 1961.
Harold Gillies died in London on 10 September 1960, survived by his second wife and by two sons and two daughters of his first marriage. Gillies had been an original thinker of great brilliance with a puckish sense of humour and a tendency to practical joking. The art and science of modern plastic surgery, in Britain and New Zealand in particular, owe their origins mainly to him.