Fylkir A
midfielder, Kolbeinn began his career in his native
Iceland in the
Fylkir academy. His progression was such that he became the club's youngest-ever player when he made his debut at age 14 years and 229 days in a 3–0 group stage
League Cup victory over
Þróttur on 11 April 2014. Kolbeinn signed a new -year contract on 2 May 2015, he became the youngest player in the club's history to start a
Úrvalsdeild match, when he made a late substitute appearance in a 1–1 draw with
Fjölnir. Kolbeinn made 15 appearances during the
2015 season and departed the
Fylkisvöllur in January 2016. The transfer made him the youngest player to sign a contract with the club. Kolbeinn moved to
England to transfer to the
B team at
Championship club
Brentford. On 17 February 2019, he won his only first team call up for an
FA Cup fifth round match versus
Swansea City and remained an unused substitute during the 4–1 defeat. which was subsequently extended by a further month. He made 15 appearances and scored two goals during his spell. he departed the club. After making 18 appearances during the
truncated 2019–20 season, he made 28 appearances and scored four goals during the team's
Regionalliga West championship-winning
2020–21 season. During an injury-affected
2021–22 3. Liga season, Kolbeinn made 19 appearances without scoring. Over the course of his time with the club, Kolbeinn was developed into a left-sided
utility player.
Lyngby On 25 January 2023, Kolbeinn transferred to
Danish Superliga club
Lyngby and signed a -year contract. He made 48 appearances and scored three goals over the course of the
2022–23 and
2023–24 seasons, After five early
2024–25 season appearances,
Utrecht On 21 August 2024, Kolbeinn transferred to Eredivisie club
Utrecht and signed a three-year contract, with the option of a further year, for an undisclosed fee. in which the club qualified for the
Europa League. Again behind El Karouani during the
2025–26 season, == International career ==