James Henry Fleming was born on July 5th, 1872 in the Toronto home of his parents on Yonge street. His father, James Fleming (1812-1887) emigrated to Canada from Aberdeen, Scotland in 1834. James Fleming, senior moved to Toronto from Montreal in 1836 and established a profitable nursery and seed growing business at the corner of what is now Yonge and Elm Streets. In addition to being a successful businessman, James Fleming was active in public affairs. He was a justice of the peace for the city of Toronto and county of York, alderman for St. John's Ward 1877-80, and a director of several agricultural societies. Following the death of his first wife (Margaret Geddes), James Fleming married Mary Elizabeth Wade (1833-1923) of Port Hope, Ontario in 1869. The only surviving child of this union was James Henry Fleming. There was, however, a half-sister, Isabella (1839-1883), from his father's first marriage.
J.H. Fleming attended the Model School in St. James Square and subsequently graduated from Upper Canada College in 1889. He obtained no formal secondary education, although he did attend a mining school in London, England for a brief period. He married Christine Mackay Keefer (1867-1903) of Rockliffe Park on December 8, 1897 and together they had his only two children, Annie Elizabeth (1899-1946) and Thomas Keefer (1901-1988). Following the death of his first wife, he married Caroline Toovey (1876- 1958) of Towersey, Oxfordshire, England on 1908. J.H. Fleming was independently employed in the management of his father's Elm and Yonge Street properties, which he inherited in 1897. This arrangement allowed him the time and financial freedom to pursue his love of ornithology as a true amateur.
J.H. Fleming began cultivating his natural history interests at a very young age. His first interest was in the plants and butterflies of the Elm street garden, but, by the age of twelve his passion had settled on birds. The earliest specimens in his collection date from 1884 and he was known to have purchased hummingbird skins with his lunch money while still in primary school. An 1886 visit to London and the Natural History Museum with his father convinced him to begin an ornithological collection. In 1905 J.H. Fleming had the first of two additions built onto his home at 267 Rusholme Road to house the growing collection. The collection and library eventually occupied a three-storey addition and was comprised
of 32,267 specimens representing all of the 27 known orders of recent birds, 163 out of 166 families, 2074 of 2600 genera, and over 6300 species (based on the taxonomy at the time of his death), plus approximately 10,000 library items. At the time of his death, the collection was believed to be the largest and most representative private collection of birds in the world.
Many awards and honours were bestowed upon J.H. Fleming during his life time including the following: Honourary Curator of Ornithology, National Museum of Canada, 1913; Honourary Curator of Division of Birds, Royal Ontario Museum, 1927; Honourary Member Societe Ornithologique & Mammalogique de France, 1931; first Canadian president of the American ornithologists' Union, 1932; corresponding Member of the Zoological society of London; Colonial Member of the British Ornithologists Union. In addition, J.H. Fleming published more than 80 scientific notes and papers and presented many others at the meetings of the Brodie Club, Toronto Ornithological Club and Toronto Field Naturalists Club.
James Henry Fleming died in his home on 27 June 1940 of natural causes. On March 20th, 1928 he had written a codicil to his will leaving all of his ornithological collection and scientific library to the Royal Ontario Museum. The bequest placed the Royal Ontario Museum among the leading ornithological collections in North America.