For nearly thirty years, the Urban Planning and Renewal Agency (URPAM) has undertaken to rebuild and requalify swathes of central urban areas of a large French Mediterranean city, in what is now considered the largest urban renewal operation of a city center in Europe. Firstly, this case illustrates how this small public project administration, with an initial technocratic culture, was led to strengthen and enrich its consultation practices in urban development beyond the legal requirements, to establish denser interactions with local communities, and finally to reinvent through trial-and-error a language of participation based on temporary urbanism, local initiatives, and the projects of local and future residents (Moore 1995; Soldo et al. 2019). Secondly, the case study reports the events, trajectories and implementation strategies of these participatory approaches seen as social innovation phenomena both within AARU and across its interactions with its stakeholders. The development of the innovative practices is rendered as a story of experimentation, learning, and institutionalization over the last twenty years, across multiple and successive urban project areas. Causal analysis was used to unveil the drivers and barriers identified by the actors, which range from various resources to gaining support in a legitimizing arena (rather than an authorizing environment), but also political cultures, politicization, and community resources and perceptions. This case study applied the methodology of the European research project H2020 COGOV to: (a) qualify the development of URPAM's participatory innovations according to the major schools identified in public management and (b) identify the barriers and drivers for the emergence of these innovations. From July to December 2019 we conducted 12 semi-structured interviews, two of which were exploratory and ten of which followed the COGOV unified interview guide. Half of the interviews involved agency staff in various positions (project managers, management positions), while the others involved key subcontractors (mediators) for the innovative practice, local residents and NGO representatives, an institutional stakeholder and project beneficiary, and an institutional partner (state). Secondary data were also used: successive strategic plans, promotional materials, calls for initiatives, institutional websites. Content analysis and causal analyses were used to identify the enabling and blocking factors for innovation. We find that, in order to move away from its traditional and technocratic urban planner’s role and to develop an innovative practice of co-production, the agency relies on a strong organizational culture and forms of strategic learning. Post-NPM models of public management such as New Public Governance (NPM) and co-production are present, as well as an invariable recourse to the French doctrine of General Interest. Overall, these analyses encourage the idea that the challenges facing public organizations, local innovation, and organizational learning can induce interesting organizational idiosyncrasies across French public administrations.