The purpose of this research is to introduce a qualitative sustainability performance assessment framework for food supply networks, based on the perception of their key stakeholders’ upper management. Moreover, the paper provides industry insights by exemplifying the value of the proposed framework for the UK food industry. A critical review on the most acknowledged sustainability assessment methodologies and tools resulted in the synthesis of the proposed framework. An illustrative application follows, based on data from semi-structured interviews with C-level executives from key players of the UK poultry sector. The results demonstrate an easy-to-use approach, with a comprehensive and sharp outcome on supply chain sustainability performance assessment. Industry insights demonstrate an adequate sustainability performance with respect to the entire supply chain. A detailed view on different echelons reveals specific areas that could be improved, such as the environmental performance at both farming (production) and processing levels. This work extends the scope of current sustainability performance assessment tools by providing a tangible triple bottom-line overview, as well as echelon-specific and indicator-specific details, in a user-friendly, yet straightforward, way. UK food industry insights are valuable for practitioners and academics. The illustration is based exclusively on C-level executives’ viewpoint; thus, any generalization of the results should be considered to this effect. Supply chain stakeholders, policy-makers, and researchers could perform a quick and reliable supply network sustainability performance assessment.