[1][2] In 1928, he became a staff member of the New York Botanical Garden and made his first tropical trips to Colombia, Peru, and Brazil from 1926 to 1929.
[1] He later left New York City to be director of the Arnold Arboretum at Harvard and worked there until 1948 when he joined the Smithsonian Institution.
From 1962 to 1963, he was the Assistant Secretary of the Smithsonian Institution and a program director of the National Science Foundation.
Smith was elected to membership in the United States National Academy of Sciences in 1963,[4] and was a distinguished botanist who specialized in Pteridophytes and Spermatophytes at the University of Hawaiʻi until 1970.
He moved to the University of Massachusetts until 1976 before returning to Hawaii to work at the National Tropical Botanical Garden.