The 29-year-old back-row arrives following an impressive campaign with French Top 14 side USA Perpignan, where he made 13 appearances and played a key leadership role within the Catalan squad.
Prior to his move to France, Ritchie spent 11 years with Edinburgh, making 133 appearances and scoring 10 tries. Renowned for his relentless work ethic, physicality and effectiveness at the breakdown, he established himself as a firm favourite among the capital club's supporters.
A former Scotland U20 captain who also represented his country at U16 and U18 level, Ritchie made his senior international debut in a 48-10 victory over Canada during Scotland's 2018 summer tour.
Capable of operating across the back-row, he has since earned 63 caps for Scotland, featuring at both the 2019 and 2023 Rugby World Cups and captaining his country at the latter tournament.