[1] Lagergren started playing handball at his hometown club HK Varberg.

[2] A season later he joined IFK Kristianstad to play elite handball and develop further.

[6] Here he won the IHF Super Globe 2023, the DHB-Pokal and the German Handball-Bundesliga in the 2023/2024 season.

His first major international tournament was at the 2016 Olympics in Rio de Janeiro, where he was included due to Johan Jakobsson getting injured.

[7] He participated at the 2017 World Men's Handball Championship, where he once again was included due to a Johan Jakobsson injury just before the tournament.