Skar participated in FIS and junior races until 2012. Since 2012 he has mainly competed in the Scandinavian Cup , which he finished fourth in 2013 and third in the overall ranking in the 2014/15 season. At the European Youth Olympic Festival 2009 he won gold over 7.5 km classic and silver in the sprint. At the Junior World Championships in 2011 in Otepää , he won gold with the relay and over 10 km freestyle. His first World Cup race ran in February 2011 in Drammen , which he finished in the sprint with 28th place and thus won his first World Cup points. At the Junior World Championships in Erzurum in 2012 , he won silver once and bronze three times. In March 2013 in Lahti he achieved tenth place in the sprint, his first top ten place in a World Cup individual race. In January 2015, he finished eighth in the sprint race in Rybinsk . At the U23 World Championships in Almaty in 2015 , he won silver in the sprint. In March 2015 he achieved his first World Cup podiums with second place in the sprint in Lahti. In the 2015/16 season he finished in the top ten in all three sprint competitions in the World Cup and thus finished 21st in the Sprint World Cup. After finishing third in the sprint in Davos at the beginning of the 2016/17 season, he won his first sprint World Cup victory in Toblach in January 2017 . He also achieved third place in the sprint in Falun and third place in the sprint at the Scandinavian Cup in Lahti. At the season highlight of the Nordic World Ski Championships 2017 in Lahti, he came in 13th place in the sprint. At the end of the season he was fourth in the World Cup finals in Québec and reached 16th place in the overall World Cup and third place in the Sprint World Cup. In the 2017/18 season he finished in the top ten three times in the World Cup. He achieved second place in the 15 km mass start race in Oberstdorf and, at the end of the season, 29th place in the overall World Cup and 11th place in the Sprint World Cup.
After 23rd place at Lillehammer at the beginning of the following season, Skar won the sprint race in Dresden and the team sprint together with Erik Valnes . In February 2019 he finished second in the team sprint with Eirik Brandsdal in Lahti and seventh in the sprint at the 2019 Nordic World Ski Championships in Seefeld in Tirol . At the end of the season he achieved third place in the sprint in Falun and Quebec and ninth place overall at the World Cup finals in Quebec. He finished the season in 11th place in the overall World Cup and fourth in the Sprint World Cup. In the 2019/20 season he took 16th place in the Ruka Triple and second place in the sprint in Dresden. He also won the team sprint in Planica together with Erik Valnes and at the end of the season he finished 24th in the overall World Cup and tenth in the Sprint World Cup.
Norway
Toblach
Dresden
Planica
Madona
Joulumae
Vuokatti