NGOs are expected by their social mission not only to assess but to report on sustainability issues in response to the growing public awareness of the sustainability agendas. Since NGOs are globally renowned as watchdogs for advancing socio-economic development and sustainable societies, research on their efforts in this regard will help develop recommendations on how they can be better positioned as the watchdog. The purpose of this article is to review and assess the understanding of sustainability (reporting) in NGO literature as well as the barriers and drivers. The study investigates various practices of sustainability and identifies the drivers and barriers in sustainability reporting (SR). The authors reviewed 61 articles published between 2010 and 2020 on sustainability and assessed the strengths and weaknesses in the understanding of sustainability in literature as well as the reporting phenomenon in NGOs. The misconceptions in the definition of SR tend to weaken its relevance and applicability, and the reporting process is often focused on demonstrating the legitimacy of NGOs rather than improving their performance. As such, it provides more evidence in support of the need for a more holistic and all-inclusive definition that will aid regulation and enforcement. We also found that, although it is often assumed all NGOs share similar objectives, it is not always the case as there are as diverse objectives as there are numbers of NGOs and their reporting pattern varies in accordance with this diversity. The review makes a case for a more comprehensive definition of SR suitable for NGOs using four elements as well as providing suggestions for where research in this area might focus to enhance the overall body of knowledge. The study contributes to theory and practice by introducing new elements guiding the definition of SR in NGOs which supports accountability and proper functioning of a circular economy and promotes sustainable development.