He has been politically active in the Centre Party and Nei til EU since 1992. In 1995, he became a member of Naustdal municipal council and Sogn og Fjordane county council. In 1996, he walked 440 km on foot from Oslo to Loen in protest against the fact that as a student in Oslo he was not allowed to cover travel expenses at municipal board meetings. The case ended with County Governor agreeing with Gjelsvik that he should have his travel expenses covered. Gjelsvik sat on the county board for the Centre Youth in Sogn og Fjordane from 1992 to 1995 and on the Centre Youth's central board from 1994 to 2000. He was the Centre Youth's political deputy leader from 1997 to 1998 and leader from 1998 to 2000. He was also leader in Nei til EU from 1999 to 2004.
