National policy initiatives are faced with challenges in their partnership development and sustainability. The National Dementia Strategy for England recommended Dementia Adviser (DA) and Peer Support Network (PSN) services and 40 demonstration sites were established. In this paper, we report on the national evaluation of these demonstration sites, with specific reference to aspects of organisational development. The research used a mixed-methods design with three main strands: (i) activity and outcome monitoring; (ii) organisational surveys and collaborative discussion; (iii) in-depth case studies in eight of the 40 sites. This paper focuses primarily on three rounds of organisational surveys distributed to all 40 demonstration sites over a period of 21 months and interviews in the case studies. Data identify the significance of infrastructure within immediate services as well as the position of services within the external infrastructure of the wider health and social care landscape. Partnership – both internally and externally – was key to establishing and sustaining services that flourished. When working well, DAs and PSNs acted as a link between services and people with dementia at the same time as filling gaps in existing support, providing information, advice and interpersonal support that was tailored to individual needs and circumstances. In conclusion, to achieve the full potential and sustainability of services requires them to be in an organisational space that allows them to work in partnership and collaboration with other services, and that values their distinct knowledge of their communities.