The Great Green Wall Initiative (GGWI) is a pan-African program launched in 2007 to combat land degradation and bring about both ecological and socio-economic benefits in the Sahel. With projects in place on only one-fifth of the targeted land and uncertainty about the extent of positive impacts, there is a need for improved monitoring and evaluation of current projects to inform the design of future projects. In this paper, we focus on the evaluation of socio-economic impacts, drawing on development theory, to relate investments in sustainable land management (SLM) to outcomes in terms of human well-being. We deploy a conceptual model, which draws on both the capability approach to human development and the sustainable livelihood framework. To contextualize the framework to the Sahel, we undertook a literature review of scientific studies of the facilitative social conditions and socio-economic impacts of SLM interventions in four countries: Senegal, Burkina Faso, Niger and Ethiopia. We further refined the framework by examining project evaluation reports of Global Environmental Facility (GEF)-funded SLM projects. Our analysis of GEF projects shows that current monitoring and evaluation pays only limited attention to achieved outcomes in terms of well-being. We briefly discuss the application of the framework to SLM interventions and make recommendations for how it should be operationalized, including recommending more comprehensive measurement of the well-being impacts of these projects.