Manufacturing organizations continue to face challenges related to sustainability assessment in their current production process. This study aims to develop a structured conceptual method necessary for sustainability assessments of manufacturing processes. The development of the conceptual method was performed by integrating a new group of sustainability indicators into the value stream mapping. In this context, forty empirically tested sustainability indicators were identified in triple bottom line perspectives and formulated for the development of a conceptual method. The developed method was applied in two manufacturing organizations to evaluate its applicability. The findings of this study reveal the case organizations were sustainable in customer perspectives but not sustainable in triple bottom line dimensions perspectives. Moreover, a solution approach is provided by the experts to improve the manufacturing process sustainability. The proposed approach in this study also contributes by providing a reference for operation managers who may struggle to assess and enhance sustainability. Finally, this study contributes by encouraging practitioners and researchers to broaden the study in a similar field and explore the application of value stream mapping and appropriate indicators for sustainability assessment.