[2] While still a teenager, Ritchie made his first-team debut in October 2014 with an appearance from the replacements' bench in the Pro12 match against Leinster.

[6] Ritchie received his first call up to the senior Scotland squad by coach Gregor Townsend in October 2017 for the autumn internationals.

[9] Ritchie received player of the match in Scotland's match against France in the 2020 Six Nations, after getting punched by France prop Mohamed Haouas[10] During this game Mohamed Haouas was sent off for dangerous play in the 37th minute for punching Ritchie.

In October 2022 Ritchie was named as the captain of the Scottish squad for the 2022 end-of-year rugby union internationals.

[13] In 2023 Ritchie was selected in Scotland's 33 player squad for the 2023 Rugby World Cup in France.