[5] He made his ATP Tour debut at the Sofia Open, where as a qualifier, he defeated defending champion Marc-Andrea Huesler in the first round,[6][7] before losing his next match to third seed Jan-Lennard Struff.

[12] Entering as an alternate at the Nottingham Open Challenger, he overcame Coleman Wong,[13] João Fonseca,[14] and Mikhail Kukushkin[15] to reach the semifinals, where he lost to qualifier Charles Broom.

[1][20] His good form continued at the next grass court tournament, the Eastbourne International, recording wins over fellow wildcard Jacob Fearnley,[21] lucky loser Charles Broom[22][23][24] and Flavio Cobolli to make it through to his first ATP Tour semifinal,[25][26] where he lost to Max Purcell in three sets.

[34][35] Harris started his 2025 season representing Great Britain at the United Cup in Australia, where he lost all three of his matches to Tomás Martín Etcheverry,[36] Alex de Minaur[37] and Hubert Hurkacz.

[38] Wins over Yuta Shimizu[39] and Carlos Taberner[40] saw him reach the final round of qualifying at the Australian Open for the first time, but a defeat to Kamil Majchrzak meant he missed out on a place in the main-draw.

[44] The following week he defeated Eric Vanshelboim, James McCabe, Elias Ymer and Tristan Schoolkate to reach his second Challenger final at the Delhi Open, where he lost to Kyrian Jacquet.