[1] He began his career in the youth academy of the local club Middelfart G&BK where he played alongside the likes of Christian Eriksen and Rasmus Falk.

[2] An integral part of the Vejle side in the second-tier 1st Division, in January 2013 he signed a contract with AC Horsens that would see him move in the summer transfer window.

[4] He made his debut on 2 July 2015 in a 1–0 away win over Andorran club UE Sant Julià in the UEFA Europa League, coming on as a substitute for goalscorer Jonas Borring in the 82nd minute.

[9] Marxen was appointed the new team captain of Randers on 30 January 2019, taking over the role from Nicolai Poulsen who would leave the club as a free agent for rivals AGF.

[10] The following season, he won his first trophy as Randers clinched the Danish Cup victory in a 4–0 beatdown of SønderjyskE in the final, with Marxen scoring the opening goal in the second minute.