This case study investigates the criteria for organizational effectiveness in non-profit organizations (NPOs) with the aim to determine how the elements of sustainability fit within the criteria. To achieve this, the study utilized the research questions: “what criteria do NPOs use to evaluate their effectiveness?” and “how is sustainability embedded in NPO effectiveness?” The research design was interpretivist, adopting focus group interviews to obtain data. Specifically, two focus group interviews were held with the top management of an NPO which revealed that both financial and non-financial criteria were equally essential for NPO effectiveness. This finding is consistent with the literature, although it contradicts the initial assumption of the study that NPO effectiveness was based more on non-financial criteria than financial criteria. The study also found that the effectiveness of an NPO should be viewed in two ways: firstly, “the full achievement of its mandate” and, secondly, “the ability to run business projects to cover cost.” It also emerged that both the ability to cover costs and the achievement of a mandate should be done in a sustainable manner (a sustainable manner is seen as one that is harmonious with the natural and the socio-political environment). The results of this paper present a practical case for the management of NPOs by reiterating that the full achievement of the NPO mandate and the successful running of social projects to generate funds for sustainability are key elements of effectiveness. Given the essential role that NPOs play in developing countries, this study has provided the foundation for more widespread enquiry into the sustainability and effectiveness of NPOs.