He made his senior debut with Haukar on 12 September 2016, starting and playing the full 90 minutes of a 1–1 draw with HK in the 2016 1. deild karla.

In January 2023, Dagur signed a two-year contract with two additional club option years with Orlando City of Major League Soccer.

[4] Dagur received his first senior international call-up for Iceland in November 2022 for a pair of friendlies against Saudi Arabia and South Korea.

Played outside of a FIFA window, the squad was a chance for manager Arnar Viðarsson to work with domestic players and those from other leagues not active in November.

He made his debut on 6 November 2022, starting and playing the full 90 minutes in a 1–0 defeat to Saudi Arabia in Abu Dhabi.