John Saxon Barton was born on 13 April 1875 in Richmond, Victoria, Australia, the son of John Barton, a minister of the United Methodist Free Churches who had emigrated from Lancashire in 1866, and his second wife, Ann Eliza Duncan. He started work as a bank clerk, studied accountancy, and in 1900 became an associate member of the Incorporated Institute of Accountants, Victoria. By 1903 he was manager of the English, Scottish and Australian Bank in Booleroo Centre, South Australia. On 12 December that year he married Isabel Catherine (Rene) Stacy at Clare. They immediately left on the Warrimoo for a honeymoon in the South Island of New Zealand, and then settled in Wellington. They were to raise a family of four daughters and a son.
By 1905 John Barton was actively involved in the training of accountants, as the founding director of Banks Commercial College in Wellington. Accountancy was developing rapidly as a profession and local textbooks were required. To meet this need Barton wrote Twentieth century commerce and bookkeeping (1905) and The New Zealand company secretary (1909); both became standard works and ran to many editions. A founding member of the New Zealand Society of Accountants, he was elected to its first council in 1909, serving as honorary treasurer until 1914, then as president from 1915 to 1917. While teaching accountancy at Victoria College, he studied for the professional examinations in law. In 1911 he left the Commercial College and began practising as a solicitor; four years later he became senior partner in the law firm Barton and Mazengarb.
Barton's direct involvement in the accountancy profession ceased in 1918 when he was appointed a stipendiary magistrate. Assigned first to Gisborne, he travelled over dirt tracks by horse and trap, or on horseback, to preside over courts at Te Karaka, Tolaga Bay and Ruatoria. He was said to be popular with local Māori because of his fair judgements. In 1922 he was transferred to Wanganui, holding courts at Pātea, Waverley and Hāwera. In 1928 he returned to Wellington, and the family settled in Penrose Street, Lower Hutt.
Because of his expertise in financial and legal matters, John Barton was called upon to preside over many commissions of inquiry. He proved himself to be a skilful chairman during the hearings of the 1927 royal commission on Napier harbour, which recommended the further development of the breakwater. The following year he chaired a commission on Auckland's public transport system, which led to the establishment of the Auckland Transport Board.
In March 1931 Barton was one of two commissioners appointed by the Napier Borough Council to supervise the rehabilitation and reconstruction of the town after the devastating earthquake of 3 February. Barton acted as chief administrator and town-planner, providing cautious financial management and expert planning advice, while his colleague, L. B. Campbell, directed the engineering works. Essential services, including miles of sewers and water mains, were restored, and numerous buildings were repaired or demolished and replaced. Debris was used to reclaim part of the foreshore, and lawns and flower beds were laid, beginning the beautification of Marine Parade. Barton was also chairman of the government-appointed Hawke's Bay Rehabilitation Committee, which first met in Wellington in May 1931. Its main purpose was to provide financial assistance for local businesses. The new Napier emerged as a model of town planning at a time of widespread economic depression.
The commissioners left Napier in May 1933, despite having been petitioned to stay. Barton, who declined a request to stand for the mayoralty, was made a CMG in recognition of his outstanding leadership. The following year he chaired the Commission of Inquiry into Company Promotion Methods, and in 1935 he co-authored Banking in New Zealand, a historical review of the banking system. When his retirement as a magistrate was announced in January 1937, the prime minister, M. J. Savage, commended Barton on his outstanding service both to the public and government in the financial arena. Now in his 60s, he undertook the task of salvaging the assets of the New Zealand Investment Trust, serving as a director until his retirement from public life in 1945.
John Barton was a financial expert and a skilled arbitrator, a dedicated teacher and a talented writer. Among his other interests were cricket (while in Wanganui he had coached schoolboys on a pitch in his backyard), gardening, wood-turning and photography. Of medium height and well built, he had a friendly manner and a ready wit. He was a committed member of St Stephen's Presbyterian Church, Lower Hutt, where his funeral service was held following his death at Porirua Hospital on 2 September 1961. He was survived by his wife, who died the following year, and by his children.