Geir Dahlen grew up on a farm near to the Norwegian city of Tønsberg where he used the local football pitch and ski slopes. When Dahlen was nine he took part in his first cycling race before joining the local club. In 1978 he took part in the junior road race at the World Championships in the United States, and came first in the national junior road race. After a lot of training he then joined the elite cycling ranks, spending four years with Kristiansands Cykleklubb. In 1988 Dahlen competed in the road race at the Seoul Olympics where he came 68th in a large peloton of riders who were all 34 seconds behind the race winner Olaf Ludwig.