Supplier assessment is a relevant decision-making process that aims at monitoring the progress of suppliers in relevant performance aspects and, if results are worse than expected, establishing action plans to improve performance. The works developed for assessing supplier sustainability usually lack of proper structure to monitor supplier sustainability and mechanisms to weight and consolidate performance data into a global evaluation that allows deciding if the supplier is achieving its sustainability goals up to a proper degree. This paper introduces a methodology that fills this research gap and shows a case study in the automotive sector.