He had trained in medicine in Dublin and Paris under an apprenticeship system (attending lectures and working in hospitals) but had no formal degree until he later went to Germany and in 1865 obtained the prestigious MD degree at the University of Heidelberg. While overseas he married Mary Lucas in Limerick. Back in Adelaide, he practised from his home ‘Eringa Hall’ in Angas Street, behind the cathedral (later next to the tram barn), and was also, briefly, an honorary medical officer at the Adelaide Hospital. In 1876, having become wealthy, Gunson retired and built a mansion called ‘The Acacias’ on the corner of Portrush and Kensington roads at Marryatville. But only a year after it was finished, in 1878, he sold it to Sir Edwin Smith, the wealthy brewer and mayor of Kensington and Norwood, and took his family to Europe. After Sir Edwin’s death in 1919 the house was bought by the Loreto Sisters and became Loreto Convent. Initially Gunson had intended to remain in Europe but in 1881 he returned to Adelaide and built another house in Kensington Gardens.

Dr J.M. Gunson was very active in public life and in church affairs: the leading Catholic layman of the period and the first Catholic to achieve prominence in the medical profession. He was president of the Catholic Young Men’s Society and other bodies and in 1881 was installed as a papal Knight of St Gregory the Great. He also served on the council of the new University of Adelaide. He died in 1884, aged only 59, and has a large tomb in West Terrace cemetery. One of his sons, John Bernard Gunson, was also a doctor and married into the Adelaide establishment family of Morphett. He lived in the family home in Angas Street, demolished in the 1920s. Two of his daughters married into the Britten-Jones family which was another Catholic medical dynasty. Dr Bernard Gunson gave free treatment to the sisters and boarders at the Convent of Mercy in Angas Street. Two other sons of J.M. Gunson were lawyers: one of them was a partner in the firm of Gunson & Culshaw.