In October 2017, Harris received his first call up to the senior Scotland squad by coach Gregor Townsend for the Autumn Internationals. Harris is Scottish qualified through his Edinburgh born grandmother. On 11 November 2017, Harris made his test debut at Murrayfield against Samoa. Harris started in the first Six Nations game against Wales in 2018. He scored his first try for Scotland in a game vs Italy 2019 Six Nations, scoring just minutes after making an appearance off the bench and scored the winning try for Scotland against France at Murrayfield. He appeared for Scotland in the 2019 Rugby World Cup fixtures and continued his form to play in every match for 2020 Six Nations.