A preliminary literature review of mental models and the quantum organisation clearly indicated a gap, particularly in the South African context. The gap was evident on two levels: literature fails to agree on existing definitions and there is little guidance on research methodology in the context of complexity and leadership. The aim of this study was to explore and describe the form and function of leaders’ mental models in a complex environment. A postmodernist qualitative methodology as theoretical framework and constructivism as research paradigm were employed. It was important not to be restricted and limited by a specific method. Therefore a constructivist grounded theory was used to navigate in a pragmatic manner towards answers which could best describe and interpret findings in response to the initial set of research questions. Purposive sampling was used and the population consisted of individual South African leaders and academics that do research on and write extensively about the constructs investigated. Data were obtained through intensive semi-structured interviewing. Semi-structured interviewing implies that only a few research questions were selected to guide the interview, whereas the rest of the interview was a co-constructed conversation, which yielded narratives with rich data that were systematically analysed through computer-assisted coding. An initial conceptual framework was thus created and used to substantiate the findings by means of a second literature review. It is concluded that the quantum organisation, being a leader in a complex environment, the dynamics of the mental models and the complex environment itself collectively represent a constellation of complex adaptive sub-systems, affecting one another in an interdependent manner and co-evolving accordingly. The conceptual framework describes the mindful sense-making process of a leader in a complex environment, consisting of a) an active acceptance of the current reality, b) catalytic questioning, c) letting go of, d) knowing that not knowing the solution, e) trusting what they do know, f) observing the actuality of unfolding patterns and g) realisation. Criteria for rigour, authenticity, trustworthiness and credibility were applied and demonstrated. The findings provide insight into the form and function of a leader’s mental models in the complex South African context. The practical contribution of this study specifically applies to the practice of leadership development and coaching. In addition, this study contributes methodologically to the field of mental model research by demonstrating the appropriateness of a constructivist paradigm for describing and interpreting the complexities of mental models of leaders in a complex context. Recommendations and opportunities for future research were also made.