They also contested a debut season in the GT World Challenge Europe Endurance Cup with ROWE Racing, taking a best result of fourth in the 1000 km of Paul Ricard.

[citation needed] In 2023, Harper competed as a BMW works driver, entering the opening three rounds of the Nürburgring Endurance Series and the ADAC TOTAL 24 Hours of Nürburgring with BMW Team RMG, another full season in the GT World Challenge Europe Endurance Cup with ROWE Racing, and a debut campaign in the British GT Championship with Century Motorsport.

He was crowned the 2023 British GT champion alongside team-mate Darren Leung, after two race wins and four podium finishes.

Harper was crowned the 2024 GT World Challenge Europe Sprint Cup Bronze drivers' champion alongside team-mate Darren Leung, after two race wins and six podium finishes.

(key) (Races in bold indicate pole position; results in italics indicate fastest lap) * Season still in progress.