Ulf Isak Leirstein (born 30 June 1973) is a Norwegian politician, formerly for the Progress Party and then independent, and a member of the Storting from 2005 to 2021.

[3] From 1996 to 2003, he worked as project leader at Standards Norway (formerly Norwegian Technology Centre).

[3] In 2005, Leirstein was elected to the Storting (Norwegian parliament) from Østfold, after having served as a deputy representative since 2001.

[3] In January 2018, Leirstein withdrew from all his political positions and his membership of the Standing Committee on Justice after it was revealed that he had sent multiple emails containing pornographic images and videos to members of the Progress Party's Youth; the youngest recipient, being only 14, was below the age of consent at the time.

[6] He would continue in Parliament throughout his term to 2021, moving over to the Standing Committee on Scrutiny and Constitutional Affairs.