[1] He attended grammar school in the Danville District in Contra Costa County, California; he graduated on July 2, 1892.

[citation needed] He appeared in at least two plays on Broadway between 1909 and 1912,[5] and made his motion picture debut in Cecil B. DeMille's 1914 original film version of The Virginian in a bit part.

[7]: 487 Throughout his career, Simpson worked for 12 years in road shows, stock companies, and on Broadway.

Simpson is best known for his work in the films of John Ford[9]: 69, 184  and, in particular, for his portrayal of Pa Joad in The Grapes of Wrath in 1940.

[11] Gaunt, lanky, and rustic-sounding, Simpson was a familiar character actor for almost forty-five years, particularly as a member of the John Ford Stock Company.