Petersen passed his state examination in law in 1973. Between 1975 and 1981 he was mayor of the municipality Oppegård. In 1981, he was a deputy of the Province of Akershus to the Norwegian Parliament from which he retired in 2009. As chairman of the Conservative Party Høyre he worked from 1994 to 2004. Between 2001 and 2005 he was a member of the Foreign Ministers of the second government of Kjell Magne Bondevik. Since 2009, Petersen Norwegian ambassador in Vienna.