He started out representing Great Britain as a junior and U23 rider.

[2] Nilsson-Julien started riding at Herne Hill Velodrome in 2011, aged 9, joining the VC Londres cycling club.

[3] In addition to this, he won silver medals in three other events at the 2022 British championships: in the points race, scratch and Madison.

He also took bronze in the points race at the 2024 European Track Championships in Apeldoorn.

He also won a bronze medal in the 2024 French National Amateur Time Trial Championships as well as taking the 2024 Tour de la Mirabelle (UCI 2.2).