Thoreau MacDonald was born in Toronto in 1901, the only child of Group of Seven artist E.H. MacDonald and his wife Joan. His earliest memories were of the woods near High Park, where his father could paint on weekends and he could explore the flora and fauna. His first published work, three lino-cuts, appeared in the Canadian Forum on 22 February 1922, and he continued to publish drawings and lino-cuts in it until 1932. His first book, Early Canadian Woodcuts (lately discovered), was a privately printed pamphlet, while the first commercially published book with his designs was Ben King's Verse in 1923, for which he did the lettering on the title page, cover, spine and jacket.
Although there is Thoreau MacDonald material in several other institutions and in private collections, the Fisher Library is the principal archival source for his career as a graphic artist.