This study proposes a sustainability maturity model tailored to small and medium-sized enterprises (SMEs) and validates it using data from 409 Canadian firms. Sustainability practices are assessed across three dimensions: environmental management, human resources, and community involvement. Using Principal Component Analysis and K-means clustering, we identify four maturity levels, ranging from Apprentice to Structured, and confirm them through Random Forest classification. Results reveal non-linear progression and uneven development across dimensions. The model serves as a self-assessment tool for SMEs and offers insights for policymakers. Future research should incorporate economic sustainability and explore sector-specific adaptations.