Thomas Johnson was born in Dunedin. His father was William Plummer Johnson a civil engineer and his mother Charlotte New Zealand Johnson, nee Jefcoate. He was educated at Thames High School and Auckland Grammar School proceeding to Otago University with a junior entrance scholarship. Undergraduate years were very successful, with every possible prize including the medical travelling scholarship and the presidency of the students’ association. He was a hockey blue and represented Otago in this sport.

On graduation in 1909 he was appointed to the house staff of Dunedin Hospital and later the Middlesex Hospital, London with Dr Essex Winter, and to Maida Vale with Leonard Guthrie and Wilfred Harris. From Harris he learnt the technique of fifth nerve injection for trigeminal neuralgia, a procedure he often performed later in Auckland. He gained his MRCP in 1911.

Johnson returned to New Zealand and wrote an MD thesis on the apex beat. He settled in Napier and was appointed to the honorary staff of the Napier Hospital. For ten years he was in a general practice which included surgery and obstetrics. He returned to London for postgraduate work in medicine at the Middlesex Hospital with Izod Bennett. Whilst there insulin was discovered and Johnson sent some back to Napier to treat a very ill young man. This was the first use of insulin in New Zealand. Returning to New Zealand in 1921 he set up a consulting medical practice in Auckland and was appointed honorary physician to Auckland Hospital, a position he held with great distinction until he retired in March 1951. In 1932 he was elected FRCP and in 1938 was a foundation Fellow of The Royal Australasian College of Physicians, becoming its vice-president and censor. He also was examiner in medicine for the University of New Zealand. He was appointed consulting physician to the New Zealand Navy, member of the General Medical Council, chairman of the Miners’ Pension Appeal Board and chairman of the Dominion Tuberculosis Committee. He played an active part in the foundation of the medical library at the Auckland Hospital, the formation of the Auckland Clinical Society and the Cancer Consultation Committee.

Dr Johnson soon developed an immense consulting practice. In parallel with this he was a keen angler and became a life member of the Auckland Acclimatization Society. Most of his vacations were spent at Taupo trout fishing - at which he was very skilful. He was a member of the Auckland Golf Club, playing a very sound game. It was at the Middlemore Golf Club that he suffered his initial infarction. He also belonged to the Northern Club. Gardening was an absorbing hobby to him, as also was Maori history, folklore and language. He could talk with some authority on native flora, fauna and the wild bird life of New Zealand. He was a fit man and a natural athelete.

To the general practitioner he was the ideal consultant, quick, simple and to the point. In court work he was an excellent expert witness and was held in high esteem by the judiciary. To the young man entering practice Johnson was most helpful. He began his rounds punctually and delighted in having visitors with him. He usually had a group of chronic outpatients who loved him and attended for years and with whom he was understanding and compassionate. He made a major contribution to postgraduate medicine in New Zealand. On retiring in 1951 from the visiting staff he was appointed consulting physician and sat on the committee on appointments. In 1952 he suffered a severe illness from which he never completely recovered. He continued work but in a reduced measure. He celebrated his sixty-ninth birthday with his family and the next morning was seized with his last illness. He was survived by his wife and twin sons, both of whom entered the medical profession.