Longman was born at Heytesbury in Wiltshire, England, and educated at Emwell House School at Warminster.
There he, with support from local businesses, established a newspaper first called the Rag, and later the Citizen.
In 1904 he married Irene Maud Bayley, who was to be the first woman elected to the Queensland Parliament.
Interested in the natural history of the area, Longman collected botanical specimens and helped establish the local field naturalists club.
There the main focus of his interests turned from botany to zoology, especially vertebrate paleontology, describing new genera of fish, marine reptiles, dinosaurs and a marsupial.