[1][2] Dagur began his senior handball career at local club Valur in 1990, having passed through their youth system.

That same year, he became the head coach of the Austrian men's national team, before joining German club Füchse Berlin in 2009.

In 2014, he won the DHB-Pokal with Füchse Berlin, the club's first major trophy, and became the head coach of the German men's national team.

Dagur won the EHF Cup with Füchse Berlin in 2015 and left the team following the conclusion of the season.

Dagur won the 2016 European Championship with the German national team and earned the bronze medal at the 2016 Summer Olympics.