Abstract Town centres—the traditional hearts of European cities—remain dominated by retail use-classes. Recent changes in consumption, digitalisation, and sustainability concerns have revealed the limits of mono-functional high streets, leading to reduced footfall, growing vacancies and declining social vibrancy. At the same time, large-scale properties such as former department stores, once considered stable investment products, increasingly face financial risk and obsolescence. Existing research highlights the potential of mixed-use and vertical mixed-use developments to reverse these trends, yet quantitative optimisation studies remain scarce and rarely incorporate citizen preferences alongside investor objectives. This study addresses this gap by proposing a conceptual and participatory optimisation framework for allocating different use-classes within existing multi-storey town-centre buildings. The framework combines the economic objectives of property owners with the preferences of local users. These heterogeneous inputs are embedded in a mixed-integer non-linear optimisation model, implemented in PySCIPOpt and solved using a spatial branch-and-bound algorithm. An empirical survey conducted in Germany provides the basis for capturing citizen preferences regarding different types of uses. The findings suggest that viable town-centre revitalisation requires a diversified combination of functions, in which retail continues to play a role but must be complemented by food, workspaces, leisure, services and healthcare. Residential use, despite strong demand among citizens, is often constrained by economic feasibility and compatibility considerations, underscoring the trade-offs between financial returns and urban vibrancy. This study contributes theoretically and practically by providing a reproducible, data-driven optimisation model for vertical mixed-use redevelopment. It demonstrates that integrating investor and citizen perspectives can generate locally specific and economically viable use-class scenarios. The framework offers guidance for real estate investors, urban planners and policymakers seeking to revitalise town centres through resilient and sustainable mixed-use strategies.