Citizenship and dementia studies have, during the last 15 years, grown into a substantial body of research recognising the experiences and agentic powers of people living with dementia. This article aims to contribute to and extend this research field. We undertake the aim through a feminist posthumanist non-representational analysis of a diary written by a man with Alzheimer's disease to explore the diary's potential to enact citizenship. The first section of the article examines current approaches to democracy, citizenship and dementia, and advances the concept intra-active citizenship, an approach that extends the individual and understands citizenship as enacted in and through entanglements of human–more-than-human agents. The second section is a theory-informed analysis of the diary, in which events, relations, doings and affective resonances constitute the analytical categories. The third section discusses whether the diary and the writing of it might enact citizenship, and if so, what kind of citizenship. The article concludes with a reflection on how our posthumanist, non-representational approach might pave a new path for theorising and, hence, contribute to new understandings of dementia and citizenship.