Interventions to improve the sustainability and nutrition of food can be misdirected when based on assumptions about people’s priorities and level of knowledge. When citizens have the capacity to act on their own priorities — in other words when they have agency — there is the potential to achieve better and more durable outcomes. This paper highlights lessons and insights gained from the Sustainable Diets for All (SD4All) programme about the opportunities, dilemmas and tensions of putting citizen agency — with an emphasis on low-income citizens — at the centre of advocacy and interventions, when supported by external development agencies. The paper situates those insights within the wider context and literature.