Digital transformation (DT) is crucial for SMEs to streamline operational efficiency, foster innovation, and meet upcoming challenges. Integrating sustainability into this process not only enhances a company’s reputation but also attracts customers and investors who value environmental responsibility. Despite this opportunity, many SMEs operate without clear plans and strategies. The literature review identified a lack of roadmaps that integrate sustainability into the digital transformation process for SMEs. Thus, this paper aims to propose a sustainable digital transformation roadmap for SMEs that evaluates their digital maturity and facilitates gradual implementation in alignment with their strategic objectives. A systematic literature review using the Methodi Ordinatio defined six key dimensions of digital transformation. Consequently, the SDT-SMEs Roadmap was developed, drawing on ISO/IEC 33000 standards to offer well-defined processes for enhancing digital competencies. The roadmap features three organizational planning levels—strategic, tactical, and operational—and includes a maturity model that evaluates 75 processes across six dimensions: Digital Technologies, Customer Focus, Organizational Culture, Organizational Governance, People, and Sustainability. Validation through a case study confirmed the roadmap’s effectiveness in addressing real-world challenges and guiding SMEs through the digitization process. The SDT-SMEs Roadmap provides a comprehensive and integrated approach, ensuring continuous adaptation and improvement in sustainable digital transformation efforts. This roadmap addresses a significant gap in the literature and presents a practical, strategic, and adaptable pathway for SMEs embarking on their digital transformation journeys.