Birger Vestermo began competing in cross-country skiing in the 1950s and by 1955 was making a name for himself at the Norwegian national championships. His successes led to him being selected to represent his country in the 50 kilometers event at the 1956 Cortina d’Ampezzo Games, where he was disqualified in the 50 kilometers. His greatest success came when he won the inaugural edition of the Reistadløpet in 1958, but he retired the following year as a younger generation of skiers was rising on the national scene. By career he was an agronomist and later owned a farm, but he continued to ski into his 90s.