Nicholas Mickelson began his professional career at
Hamarkameratene. On 23 May 2015, He made the first-team debut as a substitute in the
Norwegian Second Division match against
Molde 2. Mickelson joined the
Norwegian top-flight club
Strømsgodset on 1 January 2019. On 30 August 2021,
Danish Superliga club
Odense BK confirmed that Mickelson would join the club on 1 January 2022 on a free agent, when his contract with Norwegian club, Strømsgodset expired. Mickelson signed a pre-contract until June 2025. However, on 31 August 2021 OB confirmed, that Mickelson would instead join the club with immediate effect. He made 102 appearances for Odense BK. In July 2025, Mickelson signed a two-year contract the German
2. Bundesliga club
SV Elversberg. He made his debut for SV Elversberg as an 81st-minute substitute in their third league match of the season against
Kaiserslautern. Mickelson made his first start in the 4–0 win against
Magdeburg on 5 October 2025, providing the assist for the first goal by
Bambasé Conté in the 23rd minute. ==International career==