Petros Bagalianis (; born 6 February 2001) is a Greek professional footballer who plays as a centre-back for German club Alemannia Aachen.
In summer 2022, Bagalianis moved on loan to PAS Giannina, the main club in the city of Ioannina. On 12 January 2023, Bagalianis returned to Olympiacos B.
On 27 August 2024, Bagalianis joined Polish top-flight club Stal Mielec on a deal until the end of the season, with a one-year extension option. On 9 January 2025, after making five league appearances for Stal, he left the club by mutual consent.
On 29 January 2025, Bagalianis signed with Super League Greece 2 club AEL on an eighteen-month deal.
On 8 January 2026, Bagalianis joined Alemannia Aachen in German 3. Liga.
Olympiacos