Braathen is the son of a Norwegian and a Brazilian . He learned to ski at the age of three, but at the age of nine he began to pursue a career in skiing. He received his training at the ski school in Oslo . As a 16-year-old he took part in FIS races for the first time in December 2016 . Due to good results at this level, he was able to play his first appearances in the European Cup a year later . Also in December 2017 he achieved his first victory in an FIS race, eight more victories followed by the end of winter 2017/18.
At the 2018 Junior World Championships in Davos , Braathen won the silver medal in the team competition , and the best result in an individual race was sixth place. On December 5, 2018, he achieved the first European Cup podium finish with second place in the giant slalom in Funäsdalen . Just three days later, on December 8th, he made his debut in the World Cup . With starting number 60, he drove in the giant slalom in Val-d'Isère on rank 26 and won World Cup points straight away. His first European Cup victory followed in Andalo on December 18, 2018, followed by two more in January. At the 2019 Junior World Championships in Val di Fassa , he won the silver medal in the Super-G and the bronze medal in the combination. With a total of three victories and three further podium places, he won the giant slalom classification of the European Cup in winter 2018/19.
Braathen experienced a rapid rise in the 2019/20 World Cup season . At the start of the season, at the giant slalom in Sölden on October 27, 2019, he surprisingly finished sixth and thus achieved his first top 10 result. On December 23, 2019, he finished fifth in the parallel race in Alta Badia , and fourth in the slalom in Kitzbühel on January 26, 2020 (after the best time in the first run with start number 34).