Stergiou initially made his competitive debut for the senior
St. Gallen side on 6 February 2019, participating in a 3–1 victory against
FC Zürich. On 22 August 2023, Stergiou joined
VfB Stuttgart in Germany on loan. Stergiou played just 39 minutes in the first half of the season, but made his first start in February and then became a regular starter. On 4 May 2024, he scored his first
Bundesliga goal in a 3–1 win over
Bayern Munich. On 15 May 2024, the loan deal was made permanent and Stergiou signed a contract until June 2028 with VfB Stuttgart. On 15 January 2026, Stergiou joined
1. FC Heidenheim on loan for the remainder of the season. ==International career==