[1] Buchanan was born in Dunbartonshire, Scotland, and in his early life apprenticed as a calico pattern designer,[2] then was foreman of a drawing shop, with a hobby of botany.
[3] In 1862 Hector employed Buchanan as a botanist and draughtsman for his survey of Otago and the West Coast of the South Island.
[1][2] When the Geological Survey and Colonial Museum (now the Museum of New Zealand Te Papa Tongarewa) was established in Wellington in 1865 with Hector as its director, Buchanan was employed[2] in the same role he had in the earlier survey.
[4] Buchanan never married and was a prodigious worker, often being at the museum until late at night.
[1] Buchanan had some 29 publications in the Transactions and Proceedings of the Royal Society of New Zealand, including his identification of new species.