The building sector is a major contributor to greenhouse gas emissions. Therefore, reducing construction activities’ global warming potential (GWP) is essential in mitigating the sector’s environmental impact. This work presents a novel Performance Generative Design System (PGDS) to promote circular design processes towards low-carbon architecture. The PGDS supports architectural design workflows that aim the reuse of building materials in the creation of low-carbon structures. Using a co-simulation approach, the PGDS integrates validated Life Cycle Analysis (LCA) and Building Energy Simulation (BES) tools to evaluate environmental impacts, and includes a custom packing algorithm to optimize material reuse. The system’s modular structure allows flexible application to various design scenarios, enhancing the potential for performance-based, low-GWP building designs. The authors tested the system in a hypothetical design of a 4-story office building located in Horsens, Denmark. The proposed PGDS generated designs that maximize building material waste usage and minimize building energy consumption and cradle-to-grave GWP, resulting in up to 18% savings of CO2 equivalent emissions. Finally, the authors discuss the current limitations of the PGDS related to its packing and material distribution abilities and building performance criteria to suggest future improvements.