Buildings are responsible for a significant portion of global energy use and carbon emissions, making green retrofits a critical strategy for achieving sustainability targets. While new buildings can be designed for high performance, existing buildings require periodic retrofitting to maintain efficiency, safety, and occupant comfort. This study proposes a structured method based on the Analytic Network Process (ANP) to holistically evaluate the performance of retrofit projects in commercial buildings. The model integrates multiple key performance indicators (KPIs) across environmental, economic, health and safety, and user-oriented aspects. A real-world case study in Hong Kong demonstrates how the method supports decision-making and post-retrofit evaluation, offering facility managers a practical and adaptable tool to align project outcomes with sustainability, compliance, and operational goals. The case yielded a Building Retrofit Performance Index (BRPI) score of 4.37 out of 5, confirming the model’s practical utility.