Einarsson made his World Cup debut at the 50 km freestyle mass start race in Oslo in March 2010 , where he finished 32nd. In December 2010 he took part in the Tour de Ski 2010/11 , which he finished 30th. He was able to achieve 18th place on the 20 km mass start stage in Val di Fiemme , which was carried out in the classic technique. Einarsson managed to place another point in the Tour de Ski 2012/13 , in which he reached 29th place on the sprint stage in Val Müstair ; However, he did not take part in the subsequent pursuit stage and did not end the tour. At the Norwegian Championships in 2012 in Voss , he won silver in the 30 km skiathlon race. In the Scandinavian Cup , in which he also won a race, he finished fifth in the 2009/10 season and second in the overall standings in 2012/13 . At the Nordic World Ski Championships 2017 in Lahti , he finished 43rd over 15 km classic and 39th in the skiathlon . The following year he ran the 15 km freestyle at the Winter Olympics in Pyeongchang and 56th place in the skiathlon, and in March 2018 he won the 45 km classic at Blåvegenløpet. In April 2018 he was Icelandic champion over 10 km classic and in 15 km mass start race in Reykjavík and in April 2019 in Ísafjörður champion over 10 km freestyle, 15 km mass start race and sprint. At the Nordic World Ski Championships in 2019 in Seefeld in Tirol , he finished 43rd in the classic 15 km race, 37th in the skiathlon and 18th in the 50 km mass start race.