This research explores how the ABCD Process, a strategic planning approach within the Framework for Strategic Sustainable Development, supports the development of key competencies in sustainability in professional practice. Addressing a persistent gap between academia and professional settings, the research adopts a qualitative methodology with semi-structured interviews with two leading experts and 14 practitioners from diverse sectors and experiences. Findings indicate that the ABCD Process facilitates the cultivation of all eight KCs with varying prominence and context-dependence. Planning Competencies emerge mostly in specific steps, e.g., the A-Step fosters Systems, Futures, and Values Thinking, while the D-Step supports Strategies Thinking. In contrast, Interpersonal, Intra-personal, and Integration Competencies develop across the whole process. Implementation Competency was least supported, often requiring additional steps for its activation. Practitioners highlighted the flexibility of the ABCD Process but also shared different views on recognizing competencies. Experts emphasized the process’ theoretical grounding in transdisciplinary, stakeholder-driven designs. Limitations include a deductive design that may constrain emergent themes, uneven familiarity with key competencies among interviewees, and absence of standardized competency assessment. Future research could explore co-designing ABCD Process adaptations with practitioners to enhance specific competencies and develop robust, context-sensitive evaluations.