Sustainability is a challenging issue for livestock production, with many expectations from citizens and consumers. Thus, in order to improve existing production systems or design new ones, there is a need for sustainability assessment tools. We propose here a method based on a participatory approach to assess the sustainability of chicken supply chains. A participating group composed of various French stakeholders (poultry industry operators, research and development scientists, non-governmental organizations, etc.) was consulted to gather the various existing visions of sustainability. Each decision was validated by this group, and this resulted in the creation of a consensual assessment grid, based on economic, social, and environmental pillars, summarized in 9 goals, 28 criteria, and 45 indicators. Each item was weighted by the participating group according to their relative importance. The grid was then tested on two different French supply chains, producing either free-range or conventional standard chickens. The strengths, weaknesses, and improvement margins of each supply chain were identified. For conventional standard production, an improvement scenario was proposed, based on changes in chicken feed and the renovation of chicken houses. This new supply chain improved many criteria in the three pillars; such as economic competitiveness, European protein autonomy, social acceptance, and lower greenhouse gas emission. In conclusion, this method provides a robust and powerful tool to help stakeholders to start their own autonomous improvement process, and thus progress towards a more sustainable chicken production.