Retrofit is typically framed as a technical intervention in existing buildings aimed at improving energy performance and reducing emissions. Yet the act of retrofitting also reorganises social relations, skills, material flows, and everyday practices, with implications that extend beyond the household to neighbourhoods, supply chains, and regional ecologies. This paper reframes retrofit as a participatory design practice that cultivates ecological citizenship, a distributed capability to learn, make, organise, and steward ecological relations through the built environment. We ground this argument in three design-led cases: (1) The Wild House (University of Brighton), a regenerative retrofit “show home” in social housing that prototypes an Ecology of Things (EoT) linking occupants, materials, and multispecies habitats through sensorial interactions; (2) Ag. Lab (University of Exeter), a bioregional, distributed manufacturing model enabling off-season farm-based production of plant-based insulating blocks using existing agricultural skills and machinery; and (3) Unlocking retrofit uptake through community champions (SEI), a street-by-street engagement and finance model that mobilises trusted local actors, deploys accessible financing, and uses behavioural insights and GIS targeting to normalise retrofit, especially for middle-income households excluded from grants. We synthesise findings into a role-based framework, citizen-learner, citizen-producer, citizen-ecologist, community champion, and derive design implications spanning methods, tools, organisational models, and learning infrastructures. Contributions include: (a) positioning retrofit as a vehicle for sufficiency and circularity rather than solely efficiency; (b) articulating participatory toolchains for distributed material production and ecological integration; and (c) proposing governance and finance patterns that enable neighbourhood-scale delivery. We conclude with a research agenda for scaling participatory retrofit across diverse housing stocks, emphasising equity, quality assurance, ecological metrics, and long-term maintenance cultures.