In 1904, Dixon became Librarian of Harvard's Peabody Museum and has been credited for creating one of the most "comprehensive and functional anthropological libraries in the world".

Dixon studied linguistics and ethnology under Franz Boas after working with Fredric Ward Putnam to obtain his PhD at Harvard.

He also carried out ethnographic research in Siberia and Mongolia (1901); New Zealand, Tasmania, Australia, and Fuji (1909); Mexico (1910); Himalayas, Assam and Upper Burma, the Malay Peninsula and Java, China and Japan (1912-13).

In his 1923 book, The Racial History of Man, Dixon disavowed earlier creationist polygenism while embracing a new evolutionary view of the races as coming from different fossil ancestors giving rise to different species of humans.

Obituaries by fellow anthropologists ascribed to Dixon an icy and demanding personality, with an attitude of "unsympathetic impartiality, of ruthless condemnation, or of detached approval.