He made his debut in the
Continental Cup in February 2005 in
Brotterode, scoring two 49th places over two days. His first time among the top thirty occurred in March 2006 in
Bischofshofen when he finished 28th, and his first time among the top ten occurred in March 2009 in
Trondheim when he finished eighth. He made his
World Cup debut in December 2009 in
Lillehammer and collected his first World Cup points by finishing 19th. His personal best is 249 meters set in
Vikersund on 14 February 2016. Stjernen won the
2017–18 FIS Ski Flying World Cup, becoming the first Norwegian to achieve this feat. He represented the sports club
Sprova IL and
Trønderhopp, ==World Cup==