Copenhagen A youth academy graduate of
Copenhagen, Kristiansen made his senior team debut on 4 November 2020 in a 2–1
cup win against
Avarta. He made his professional debut on 29 November 2020 in a 3–1 league win against
SønderjyskE. On 20 December 2020, four days after turning 18, Kristiansen signed a contract extension with Copenhagen which would run until December 2023.
Leicester City On 20 January 2023, Kristiansen signed for
Leicester City for a record-breaking fee of £17 million, making him the most expensive
Danish Superliga player ever. On 28 January 2023, he made his debut for Leicester as a substitute in a 1–0 away win against
Walsall in the FA Cup fourth round.
Loan to Bologna On 30 August 2023, Kristiansen was sent on a season-long loan to
Serie A club
Bologna. He made his debut for the club on 2 September, starting in a 2–1 league victory against
Cagliari. He immediately proved decisive, providing an assist for
Joshua Zirkzee's 1–1 equaliser in the 59th minute. Later, his cross hit an opposing defender's arm in the penalty area, but his teammate
Riccardo Orsolini missed the attempt from
12 yards. However, Kristiansen's shot on target in the 89th minute resulted in a blunder by goalkeeper
Boris Radunović, and
Giovanni Fabbian scored from the rebound.
Return to Leicester City Bologna did not activate the buy option in Kristiansen's loan, so for the 2024–25 season, he returned to Leicester City. On 3 December, he assisted
Patson Daka's goal in the 3–1 win over
West Ham. ==International career==