Altermagnets have recently been recognized as a distinct class of magnetic materials characterized by alternative spin-split electronic structures without net magnetization. Despite intensive studies on their single-particle spintronic and valleytronic properties, many-electron interactions and optical responses of altermagnets remain less explored. In this work, we employ many-body perturbation theory to investigate excited states and their strain tunability. Using monolayer ${\mathrm{Mn}}_2{\mathrm{WS}}_4$ as a representative candidate, we uncover a novel spin–valley-dependent excitonic selection rule in two-dimensional altermagnetic Lieb-lattices. In addition to strongly bound excitons, we find that linearly polarized light selectively excites valley-spin-polarized excitons. Importantly, these lowest-energy excitons are optically bright, making them experimentally accessible. Moreover, due to the interplay between altermagnetic spin symmetry and electronic orbital character, we predict that applying uniaxial strain can lift valley degeneracy and enable the selective excitation of spin-polarized excitons—an effect not achievable in previously studied transition-metal dichalcogenides. These generalized spin-valley-locked excitonic states and their strain tunability can offer a robust mechanism for fourfold symmetric altermagnets to encode, store, and read valley and spin information.

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• Excitons
• Magneto-optical effect
• 2-dimensional systems
• Altermagnets
• Bethe-Salpeter equation
• GW method