Andreas Almgren comes from the Sollentuna community and has a sister. At the age of 10 he started athletics, the sport that his mother also played. At first he also played soccer in addition to athletics, but decided to focus on athletics after the stress of both sports became too high. He has been competing in the 800 meter run since 2010. A year later he competed over this distance at the U18 World Championships in Lille. He survived the preliminary run, but was eliminated in 1: 52.46 minutes in the semifinals. Overall, he finished 19th. In August 2012 he became Swedish U18 champion and improved his best time over 800 m one week later to 1: 50.45 min. In 2013 Almgren was the Swedish U20 indoor champion over 1500 meters and won the national championship title over 800 meters in the same age group in the summer. At the Swedish championships for adults in September he stayed for the first time under a time of 1: 50.00 min over 800 meters in a competition. In July 2014 he competed at the U20 World Championships in the USA. He moved into the final, in which he won the bronze medal with a time of 1: 45.65 minutes. His time meant a new Swedish junior record over 800 meters, and at that time he was the second fastest time ever run by a Swede over this distance. Subsequently, a month later took part in the European Championships in Zurich. There he reached the next round after the preliminary run, but then narrowly retired as sixth in his semi-finals. Overall, he took tenth place.
In spring 2015 he also competed over 800 meters at the European Indoor Championships in Prague. After the preliminary and semi-finals, he achieved a time of 1: 47.78 min in the final, with which he finished fourth. In August first appeared at world championships . In his lead he ran the sixth fastest time in 1: 48.06 minutes and was eliminated. Overall, he landed in 25th place. In the following years he could not qualify for international championships because he had to fight with numerous injuries in the following three years, for example in 2018 on the hip. In 2019 he made the decision to focus on the 1,500-meter run to compensate for the lack of speed that he lacks in order to be competitive in the world class over 800 m. In February 2020, when he won the Swedish Indoor Championships in 7: 48.34 minutes, he set a new national record over 3000 meters.
So far, Almgren has won 4 gold medals at national championships, twice over 800 and once over 1500 meters in the open air, as well as the one indoor title over 3000 meters.