In 2018 Horsten made his single-seater debut, competing in the Australian Formula Ford Series, taking three podiums and one fastest lap to finish ninth in the championship.

Horsten made a move to the BRDC British Formula 3 Championship for 2020, where he would compete with Lanan Racing, partnering Piers Prior and Josh Mason.

[8] The Australian started his season off with two points finishes and a retirement, which came when fighting for the race lead with Brit Ayrton Simmons, at the Brands Hatch circuit.

[10] Horsten would have to wait until the reversed-grid race at the sixth round of the campaign to score his second podium, finishing third after having started from ninth place on the grid.

Horsten would make his first step into GT racing by competing in the 2022 BMW M2 Cup Germany where he'd qualify second and take his first podium in the third round at the Nürburgring.