This article presents a mixed methodological approach in project management research and details the terms and the conditions of its design and implementation. Assuming, on the one hand, that qualitative methods allow the study of complex processes and phenomena in their idiosyncrasy, and, on the other hand that quantitative methods produce a nomothetic science based on statistical regularities (Miles, Huberman and Saldana 2013). We argue that mixed methods research allows, under certain conditions and trade-offs in the design and the implementation, the achievement of these two objectives. Mixed methods research remains underutilised in the management sciences despite the advantages in comparison to mono methods (Molina-Azorin and Cameron, 2010). This underutilization is linked to the tendency of certain discipline traditions and preferences for quantitative approaches as opposed to qualitative approaches. This opposition is also linked to the incompatibility thesis of the epistemological paradigms combined with the exclusive links between paradigms and methods. The theoretical foundations of mixed methods is relatively young and there remains many questions relative to the process of design, implementation and integration of qualitative and quantitative research to which researchers new to mixed methods may be confronted with. This article presents research which was carried out in two stages and focuses on the comprehension and the explanation of the diversity and the evolution of project manager’s roles. The paper discusses and demonstrates the objectives of a research strategy based on a mixed methodological approach combining qualitative and quantitative methods and specifies the type of mixed method research according to the implementation order, the degree of combination of the two methods and the relative weight of the qualitative and quantitative methods. We propose a practical application of the theory of mixed methods that can assist and inspire project management researchers in the design and the implementation of their own mixed methods research.