Dr Arnott was born in Wyalong New South Wales in 1902 and educated at Goulburn High School. He then attended the University of Sydney as a student of St Andrew's College. He graduated MB ChM in 1925. He represented Australia against New Zealand in hockey in 1923 and captained the University hockey team in 1924 thereby, obtaining his blue. He underwent his training in psychiatry at Callan Park Hospital and Kenmore Hospital. In 1928 he was awarded the Diploma in Psychological Medicine by the University of Sydney. Dr Arnott entered private psychiatric practice in Macquarie Street, Sydney in 1933. He was a foundation member and later president of the Australasian Association of Psychiatrists, which was the forebear of the Royal Australian and New Zealand College of Psychiatrists, of which he was a foundation fellow.
Dr Arnott was invited to become a foundation fellow of The Royal Australasian College of Physicians in 1938. He held honorary appointments in psychiatry at the Royal Alexandra Hospital for Children, Repatriation General Hospital, Concord, St Luke's Hospital and Crown Street Women's Hospital. During World War II he served in the Army Medical Corps as a major and was in Darwin at the time of the air raids.
Dr Arnott was loved and respected by his many patients and all who worked with him throughout his long career as a psychiatrist. He had a most warm and friendly manner towards all, coupled with a good sense of humour. He was very supportive to junior staff and was a lecturer for the DPM students at the University of Sydney. He always encouraged his younger colleagues in his specialty. His year book in 1924 described him as 'generally popular and deservedly so' and he remained thus all his life.
He published several articles in the Medical Journal of Australia and wrote a fascinating history of his experiences in psychiatry entitled Fifty Years in Psychiatry which was published in 1980 by Wentworth Books, Sydney. He was a corresponding fellow of the American Psychiatric Association. In 1930 he married Eileen Teakle and they had a son and two daughters.