Sustainable Business Model (SBM) is a strategic approach that integrates sustainability into the core operations and values of organisations. However, scaling SBMs remains a significant challenge due to resource constraints, operational inefficiencies, and stakeholder complexities, emphasising the need for structured frameworks to facilitate this process. This paper introduces the Sustainability Scale-Up Framework (SSF), a comprehensive tool explicitly developed through a design approach to help businesses scale their operations while maintaining alignment with environmental, social, and economic sustainability principles. The SSF was developed iteratively through an extensive literature review, and semi-structured interviews with experts and practitioners of sustainable startups. The SSF's layered structure systematically addresses value creation, operational scalability, stakeholder engagement, and strategic alignment, uniquely integrating value tensions across economic, social, and environmental dimensions to guide the scaling of SBMs. The SSF was validated through a business case workshop where its practical utility based on parameters like usability, flexibility, coherence, and applicability were examined. This paper contributes to SBM, scalability, and strategic design literature by offering insights through a vision-driven framework, providing a novel methodological approach to integrate strategic design principles into scaling processes, and delivering practical tools for businesses, and policymakers to foster sustainable growth for achieving transformative impact.