[4] On 31 January 2019, Mogensen joined the B team at Championship club Brentford on a 2+1⁄2-year contract, with the option for a further year,[6][7] for a fee reported to be 2 million kr.
[8][9] On 7 December 2019, mounting injuries saw Mogensen win his maiden call into the first team squad and he remained an unused substitute during a 2–1 defeat to Sheffield Wednesday.
[17] He commenced training with the club on 7 September, but was not considered for first team selection during the remainder of the 2022 season,[18] due to the quota on the number of non-Norwegians allowed in Eliteserien squads.
[10] He made just two first team appearances prior to 1 August 2023,[21] when he departed to join First Division club IL Hødd on loan until the end of the season.
[24] On 20 December 2023, Mogensen transferred to First Division club Ranheim and signed a three-year contract for an undisclosed fee,[25] effective 1 January 2024.