From 1998 to 2000 he was the leader of the Young Conservatives (Unge Høyre), the youth wing of the Conservative Party.
In 2004, during the second cabinet Bondevik, Aarset was appointed political advisor in the Ministry of Local Government and Regional Development. He held the post until the change in government in 2005.
On the local level Aarset was a member of Hol municipality council from 1991 to 1995. During the period 1995 to 2002 he was a member of Buskerud county council.