[6] Horne made his debut for Glasgow Warriors in a friendly match against the British Army Rugby Union side on 25 September 2015.

[7] In November, 2015, Horne was loaned to London Scottish, by Glasgow Warriors, to gain more experience of playing professional rugby.

In December 2024, he scored a hattrick of tries and three conversions in the opening round of the 2024–25 Champions Cup beating Sale Sharks 38-19.

[12] Horne gained his first senior XV cap for Scotland on 16 June 2018 when playing against the United States.

[14] On 9 October 2019 Horne scored a hat-trick in a 61-0 win over Russia at the 2019 Rugby World Cup.