Haarup began riding motocross at the age of three and upon competing at his local club and his talent soon became noticed when he was beating riders on higher capacity motorcycles.

Haarup continued his journey with Husqvarna in 2017, starting the 2017 European Motocross Championship by winning both races at the opening round of the EMX125 class by a sizeable margin.

Before the end of the year, Haarup returned to the EMX250 class of the 2019 European Motocross Championship for the final two rounds, finishing third overall in Belgium and winning the first race in Sweden.

The 2020 season marked the end of Haarup's time with Husqvarna, as he was picked up by the Dutch F&H Kawasaki team for the MX2 class of the 2020 FIM Motocross World Championship.

[9] His second season with the F&H team saw Haarup compete in every round of the MX2 class of the 2021 FIM Motocross World Championship scoring consistently in all but two races but missing the overall podium throughout.

He showed good speed at times on the bike but picked up an injury at the first Indonesian round and missed the rest of the championship.

In the winter following this, Haarup was announced to have signed for the much anticipated Monster Energy Triumph Racing team for his final year in the MX2 class.

[12] His good form was carried over to the opening round of the 2024 FIM Motocross World Championship, where he was able to finish third overall in the MX2 class, securing a podium on the Grand Prix debut for Triumph.

Following this, he made his second appearance for his country at the 2024 Motocross des Nations, where his results contributed greatly to the teams eleventh place finish in the event.