The full integration of sustainability considerations into maintenance practices requires a close monitoring of maintenance impact through appropriate key performance indicators (KPIs) that take into account various sustainability aspects. However, there is a lack of a comprehensive framework of KPIs covering all the sustainability dimensions, and the few attempts to address this need are specific to certain industries and lack validation by experts in the field. Therefore, the aim of this research is to develop and validate a comprehensive and multidimensional framework of sustainability performance indicators for the assessment of maintenance impacts on the triple-bottom-line. To that end, an exhaustive list of general indicators is collected based on both international organizations standard-sets and published literature. Subsequently, this list is projected on the maintenance area to establish the pertinent indicators. Then, a validation phase is performed with a highly qualified expert panel through semi-structured questionnaires and follow-up discussions. The validated list of sustainable maintenance KPIs includes 63 indicators amongst which 34 belong to the environmental pillar and are split between various categories such as resource use, residuals, environmental compliance, etc. The social pillar comprises of 15 indicators related to occupational health and safety, training and development and customer satisfaction dimensions. Finally, the economic pillar includes 14 indicators split between economic performance and investment categories. The findings of this research provide guidance to practitioners in the field and set the foundations for conducting promising future works. A rich portfolio of future research based on the obtained results is proposed.