Jenks was born in Des Moines, Iowa,[1] and his mother gave him a trombone when he was 9 years old.

In the Cary Grant-Rosalind Russell classic His Girl Friday (1940), Jenks had his most famous role, as the cynical newsman "Wilson".

His biggest success was as Uthas P. Garvey, the skeptical, proletarian right-hand man for the loquacious English con artist "Colonel Humphrey Flack" (1953-54) in the DuMont Television Network series of that name.

[4] He portrayed Lieutenant Rodney in the DuMont series Front Page Detective (1951-52),[4]: 369-370  and he was a member of the cast of The Eddie Cantor Comedy Theater, which was syndicated in 1955.

[4]: 298  He appeared in Waldo, an unsold television pilot that aired as an episode of the anthology series New Comedy Showcase in 1960.