Brownfield is post-industrial soil resulting from different anthropogenic activities and located in urban centers of cities. Due to the scarcity of urban land and the complexity of renovating old cities, and considering that brownfield research in Pakistan is still in its infancy, defining and evaluating brownfield is necessary for solving environmental issues and promoting sustainable development. Therefore, this study aims to develop a pioneer consensus-based brownfield definition, guidelines, and an evaluation index system to evaluate brownfield redevelopment in Pakistan. Initially, a comprehensive literature review was performed to gather key elements of brownfield definitions and create an evaluation index system. These indicators were further evaluated by different experts through the Delphi Method to develop a final questionnaire. Then, data were collected from relevant stakeholders. An illustrative example using three ideal schemes (housing society, eco-industrial park, and commercial market) is described to apply the evaluation index system. A new methodology combining Triangular Fuzzy Numbers (TFNs) and Grey Relational Analysis (GRA) was introduced to assess three ideal schemes. Finally, a pioneer brownfield definition, guidelines, and evaluation index system for brownfield redevelopment were developed, and a further index system was verified through an illustrative example. The standard brownfield definition, guidelines, and established index system is based on the Pakistani context. Due to changes in rules and regulation, and different land characteristics, these findings cannot be generalized to all developing countries. Therefore, further studies must validate the results in their own context. This study will foster brownfield redevelopment implementation in Pakistan and promote sustainable development.