Jan Jakob Tønseth (1 September 1947 – 12 October 2018) was a Norwegian author, poet and translator.

Tønseth debuted as a poet with the poetry collection Kimærer in 1971, when he was only 24 years of age. He achieved broad recognition as a novelist with his trilogy about the ex-communist Hilmar Iversen (Hilmar Iversens ensomhet (1992), Et vennskap (1997) and Resignasjon og portvin (2002)). Tønseth was a member of Norwegian Academy for Language and Literature.