Sustainable energy transitions necessarily comprise both socio-technical aspects as well as important implications for social justice. However, in existing scholarship, these are mainly treated as distinct phenomena. The purpose of this paper is to outline a comprehensive approach that pulls together critical aspects of both socio-technical development and energy justice in understanding sustainable transitions. Drawing on the strengths of both sets of literature, we argue that a comprehensive approach requires analyses to account for the co-evolution of institutional change, material change and relational change, with a cross-cutting concern for multiple spatialities and normative implications. We then illustrate this approach through three brief case studies of multi-scalar solar uptake in Portugal, bringing out how justice considerations are intricately involved in the practices and politics of these concrete, broadly representative instances of sustainable energy transitions.