He was national champion twice and played on the European Tour, where his best finish was runner-up at the 1995 Air France Cannes Open.

Rojahn became a scratch player by 14, the same year he won the Trophy Topolino in Sanremo, Italy.

[2] In 1991, Rojahn won the Norwegian National Golf Championship and received the Kongepokal.

[1] In 1995, after finishing third at the European Tour Qualifying School, he played on the European Tour where he recorded his career best finish of second at the Air France Cannes Open, two strokes behind André Bossert of Switzerland.

Rojahn represented Norway at the 1998 World Cup of Golf in New Zealand with Per Haugsrud, where they tied for 23rd alongside South Korea.