Fanny Horn-Birkeland's first race was an individual in Östersund , where she finished 62nd. After the three races at the start of the season, it ran over the season but mainly in the IBU Cup 2009/10 . In her first race in a sprint in Altenberg , she just missed the podium in fourth place. At the end of the season, three more races followed in the World Cup, in which she was able to improve her best position up to 48th place in a pursuit race on Holmenkollen in Oslo . For the 2010/11 season , Fanny Horn-Birkeland belonged to the Norwegian elite squad for the first time after good performance in the preseason and restructuring in the squad after the Olympic season. In Hochfilzen , she won her first World Cup points as the 30th of a sprint.
Fanny Horn-Birkeland was able to achieve success at an early age. At the Norwegian Biathlon Championships 2007 in Folldal , she won the bronze medal starting with Karen Kristoffersen and Julie Bonnevie-Svendsen for the Oslo og Akershus region . A year later she was able to win her first title in a relay race with Eckhoff and Bonnevie-Svendsen in Stryn . In 2009 the title was defended in Lillehammer with Nicolaisen for Eckhoff in the team. In 2010 she was able to win a relay medal, now bronze, in Simostranda with Nicolaisen and Eckhoff. In addition, she won her first individual medal at national championships behind Tora Berger with silver in the mass start.
On February 19, 2017, she announced that she would end her career at the end of the 2016/17 season.
From 2008 Fanny Horn-Birkeland competed in races of the FIS and the Scandinavian Cup also in cross-country skiing.