In the youth and junior division, Njåtun won her first national title in the mid-2000s. After she was also successful in the adult segment - for example with four second places at the Norwegian Championships in October 2009 - she received her first World Cup appearances from the 2009/10 season . In November 2010 she won the Norwegian championship title over three distances (1000 meters, 1500 meters and 3000 meters) and, at the age of 19, came second for the first time at the World Cup in Berlin over 1500 meters. With a time of 1: 57.99 minutes, she was just a second behind winner Christine Nesbitt . Njåtun described this success as “a little unreal”. In January 2018 she took third place in Erfurt, again over 1500 meters; this time a second behind Ireen Wüst . In addition, there were seven other top 3 results in the team competition.
Njåtun placed in the top ten several times at major events. At the 2014 Winter Games in Sochi , she achieved her best Olympic result in sixth over 3000 meters; in the team pursuit, she retired together with Hege Bøkko and Mari Hemmer in the quarter-finals and came in seventh. Four years later followed in Pyeongchang, among other things, a seventh place over 1500 meters and tenth place in the 1000 meter distance. Njåtun won her first international medal at a major event at the 2015 World Championships in Calgary : On the 1500 meter stretch, she set the fastest time of all participants and set a Norwegian national record in 1: 52.71 minutes. After 2012 and 2013 , she qualified for the final of the best eight runners for the third time, where her performance was enough for third place overall in Martina Sáblíková's victory . After a season marked by illness, Njåtun's bronze medal - the first medal by a Norwegian at all-around world championships in over 30 years - was considered a surprise. At national level, Njåtun won more than 40 medals by 2020, securing 29 Norwegian championship titles.