Augustine Henry was born in Dundee on 2 July 1857.
Henry was educated at the Cookstown academy, co Tyrone and in Queen's college, Galway. He studied natural sciences and philosophy, graduating with a first-class degree and gold medal in 1877. While at Queen's college, Galway, he met Evelyn Gleeson who became a lifelong friend and correspondent. He then moved to Queen's College, Belfast to take a MA the following year. After this he worked for a year in a London hospital and in 1879 passed the Queen's University examination in medicine. During this time, one of his professors suggested the possibility of a position with the Chinese Customs service. For this Henry needed a medical qualification and he gained this possible at the Royal College of Physicians in Edinburgh, taking special examinations to speed up the process. By 1881, he had his medical qualification and accepted a post as a medical officer, setting out for China in the summer of that year.
Henry arrived in China at Hong Kong and then was ordered to his first posting at Shanghai. He spent the winter at Shanghai learning about the ways of the customs services and in the spring of 1882 he was assigned to the port of Ichang in the Hubei province on the Yangtze river, more than 900 miles inland as assistant medical officer. It was at Ichang that Henry started collecting plants. The area immediately surrounding the town is plains while only a few miles were the San Xia, a hundred miles of gorges filled with vegetation. Henry began to collect at the weekends as a hobby and then more as part of his duties as customs officer. After four months of collecting and struggling to name the plants, he wrote to the Royal Botanic Gardens, Kew seeking their advice. After the initial letter brought instructions on plant collecting, he wrote again offering to send them his specimens if they would identify them for him. The offer was accepted and he sent his first collection of around 1000 specimens to Kew in November that year. Henry continued to send specimens to Kew throughout his time in China and corresponded regularly with the director of the time, Mr Thiselton-Dyer. In 1888, he arranged special leave from his post to go plant collecting on behalf of Kew.
During this leave, Henry made two long journeys, one to the mountains southwest of the Yangtze and the other to the mountains in the north in the Hubei district. The main objective of these expeditions was to study the vegetables used in Chinese medicine. In addition to this, Henry also found many plants that were not known to grow in China. The areas he travelled were largely unknown to botanists and in some areas he was the western man to travel there. Although these trips were on behalf of Kew, it is unlikely that Henry was paid for his specimens. In order to recoup some of the money spent on the trips, Henry prepared several other sets of specimens which he then sold to other herbaria. In addition to these trips, Henry also was the first to employ native people as collectors on his behalf when he was not able to leave Ichang. They collected the some of the specimens that Henry sent to Kew.
In 1889, after a failed bid by Thiselton-Dyer for Henry to go collecting again, Henry was transferred to the island of Huinan. During the four months that he spent in Huinan, Henry collected 750 specimens. Henry then contracted malaria, endemic to Huinan. He was removed Hong Kong and then, after eight years in China, he returned home.
The year he spent at home was divided between Ireland and London. In London, he spent a great deal of time at Kew, staying with the Thiselton-Dyers. He also attended meetings of the Linnean Society, having become a fellow in 1888. During this year he met and married Caroline Orridge. In 1891, he returned to China with Caroline. It was a difficult journey as Caroline was suffering from tuberculosis and she was taken seriously ill on the journey. Henry was based at Shanghai and was not able to go plant collecting due to his work and Caroline's health. The Henry's then moved to Taiwan in hopes that it would better suit Caroline. Henry took up collecting again although he was disappointed with the results. He became very interested in the native people and their use of plants. His wife's health continued to suffer and in 1894, she and Henry's sister Mary set out for Denver, Colorado to improve her health. Henry was about to leave China to join them, having arranged to sell his herbarium to Harvard, when Caroline died in September 1894.
After her death, Henry returned to Europe for a year, becoming a member of the Middle Temple. In 1895 he returned to China and was once again based at Shanghai. In May 1896 he was posted to Mengzi in South Yunnan, once of the most remote posts in China. During his time at Mengzi, he studied the local people and he began plant collecting again. Here he found lilies, magnolias and many others. When he left Mengzi, he sent off 32 cases of botanical specimens. In 1898, Henry was transferred again, this time to Simao. He was now Acting Chief Commissioner of Customs. This meant that Henry had less time to go collecting and he relied more on one of his native collectors who had been with him for many years to do the actual collecting. Henry started to learn the language of the local people, the Lolos. In 1899, he became alarmed at the rate of deforestation in the province and wrote to Mr Thiselton-Dyer and Mr Sargent at Harvard about sending out a professional collector. In the end, neither sent a collector but one was sent by James Veitch & Sons, nursery owners. This collector was E H Wilson, better known as Chinese Wilson. Wilson went to see Henry when he arrived in China to learn about plant collecting in China. About the time he arrived, Henry was moved back to Mengzi again and they went their separate ways, Wilson taking Henry's plant specimens to send back to Europe when he reached the coast.
The political situation in China, which had been unsettled for many years, now became increasing dangerous. Henry became worried by this and almost resigned in 1900. This was now the time of the Boxer rebellion and later that year he had to abandon his post at Mengzi and go to Hekou. There he remained for several months. At the end of December 1900, he left China, officially on leave but in reality having resigned. He returned to London via Ceylon (Sri Lanka) where his sister Mary was then living. Much of the next year was spent at Kew working on the collections he had sent back from China. He was now a well known plant collector and it seems that it was at this time that he became particularly interested in forestry.
In 1902, when there was no longer any question of him returning to China, Henry began to study forestry at the premier forestry school in Europe, at Nancy in France. After a time, Henry began to wish for a job back in Ireland but none was forthcoming. He left Nancy before the end of the course and he then co-authored 'The Trees of Great Britain and Ireland' with H J Elwes. This huge work, eventually published in seven volumes, took several years to complete and Henry travelled all over the country to collect information. Once it was completed, he was without a set purpose and entered into the social whirl of London in the early twentieth century. In 1907 he became engaged to Alice Brunton who became his second wife on St Patrick's day, 1908. Henry also became professor of forestry at the new Forestry school at Cambridge University. In 1913, Henry got the position that he had always wanted when he was appointed to the newly created chair of forestry at the College of Science in Dublin. He continued at the college until his death in 1930 after a short illness.