There is no globally accepted definition of a sustainable bus transit system. In addition, the literature does not include a method for evaluating the sustainability of such systems. This paper begins with a literature review of evaluation criteria considered in previous studies. Then, we categorize these criteria into three major groups according to the three principles of sustainability. In the next step, the final list of criteria in each sustainability dimension is presented. We also identify various beneficiaries related to public bus transit systems. Finally, we suggest a mathematical approach that ranks and weights the identified criteria from the perspective of each beneficiary as well as all beneficiaries. This method can be used to select the final list of criteria for evaluating the network design and operations planning of a sustainable public bus system. This proposed approach is based on the Group Best Worst Method (GBWM). To test the applicability of the proposed model, the GBWM is applied to a small sample in the cities of Calgary, Canada, and Beijing, China, and the results for both cities are discussed. The results show that the definition of sustainability in public bus transit services is a local rather than a global concept.