Chevrel phases are triclinic crystal structures consisting of a refractory metals and chalcogenides, which present unique properties in many applications. Herein, structural, mechanical, dynamical and electronic properties of Fe2Mo6Se8 and Cu2Mo6Se8 seleno-Chevrel phases were theoretically and experimentally investigated. The theoretical studies revealed the mechanical and dynamical stabilities of these phases that lead to the experimental synthesis. These seleno-Chevrel phases were used for photothermal and photodynamic antibacterial and antibiofilm applications, in the absence and presence of near infrared (NIR) and white light-emitting diode (LED) illuminations on Staphylococcus aureus (S. aureus) and Escherichia coli (E.coli) strains. Fe2Mo6Se8 and Cu2Mo6Se8 displayed enhanced antibacterial activities (73.1% and 60.0%, respectively) and biofilm inhibition effects (93.9% and 88.7%, respectively) on S. aureus. For E. coli bacterium, Fe2Mo6Se8 and Cu2Mo6Se8 showed also antibacterial effects (60.0% and 67.5%, respectively) and biofilm inhibition activities (88.7% and 78.1%, respectively). The increased photothermal and photodynamic activities of Fe2Mo6Se8 and Cu2Mo6Se8 can be attributed to the enhanced ROS production, which triggered probably the denaturation of bacterial proteins and nucleic acids by producing photoinduced electrons to obtain super oxide anion (•O₂̄) radical under light irradiation. Therefore, seleno-Chevrel phases could be a good alternative for medical antibacterial surface applications. Moreover, Fe2Mo6Se8 and Cu2Mo6Se8 were also used as catalysts for photocatalytic hydrogen evolution reactions. Fe2Mo6Se8 showed 1.8-fold higher photocatalytic hydrogen evolution rate than that of Cu2Mo6Se8, which can be explained by the bonding properties of catalysts. This article paves the way that Chevrel phases can be effectively used for different photocatalytic and photoantimicrobial applications.