Kaarby first appeared internationally at the first test jumping on February 5, 1934 on the newly built Great Olympic Hill in Garmisch-Partenkirchen . There it reached the greatest distance with 70 meters in front of 5,000 spectators. Three years later he won the silver medal in the individual combination behind his compatriot Sigurd Røen at the Nordic World Ski Championships in 1937 in Chamonix-Mont-Blanc . Just under a month later he jumped the first hill record with 58 meters at the first jump on the Tremplin Olympique in Les Launes on February 21, 1937.