A fringe player after signing a professional contract, he transferred to English club Brentford in 2019 and was a part of the squad which was promoted to the Premier League in 2021.

Copenhagen and made his senior debut as a second-half substitute for Frederik Bay in a Danish Cup third round match versus Jammerbugt FC on 26 October 2016.

[1] On 7 August 2019, Roerslev moved to England to join the B team at Championship club Brentford on a two-year contract, with the option of a further year, for an undisclosed nominal fee.

[14][15] He held onto his place until the end of the regular season and through the playoffs,[16] which culminated in promotion to the Premier League after victory in the 2021 Championship play-off final, during which he assisted Emiliano Marcondes for one of the goals.

[19] Approaching the midway point of the season, mounting injuries in the central defensive positions saw Roerslev deployed in a right centre back role.

[25][26] The early months of 2023–24 mirrored that of the previous season, with injury to Aaron Hickey in late-October 2023 allowing Roerslev to take over the starting right back role.

[35] Following the withdrawal of Alexander Bah, Roerslev won his maiden call into the Denmark squad for a pair of friendly matches in March 2024 and he remained an unused substitute in both.

[15][36] Two defensive suspensions saw Roerslev win his second call-up for a Nations League A match versus Switzerland on 15 October 2024 and he again remained an unused substitute.