Background and Objective: Homeless people have an increased risk of infection of COVID-19, linked to several social, economic and environmental determinants, frequent comorbidities, as well as difficult access to social and health rights, medical coverage and overall insufficient use of healthcare. However, there is a lack of data not only concerning vaccination coverage but also the evaluation of interventions promoting COVID-19 vaccination among this underserved population in France. This study Aims to identify the associated factors of COVID vaccination uptake among people experiencing homelessness in the Greater Paris area and Marseille. Methods: This multi-center cross-sectional survey took place in Marseille and in the greater Paris area. The survey, conducted from 15/11/2021 to 22/12/2021, included a representative sample of 3811 precarious people. A conceptual framework for vaccine uptake among underserved populations was proposed by integrating the behavioral model for vulnerable populations and the COM-B model (capability, opportunity, motivation and behaviour). The model included one measured variable (mobility) and nine latent variables: health literacy, information, attitudes towards vaccination, perceived needs, social support from associations and from relatives, discrimination, competing needs and accessibility to healthcare. Results: Among the 3811 participants included in the sample, 74,5% had taken at least one dose of the vaccine. The main factors associated with vaccine uptake were attitudes towards vaccination, type of housing, vaccination history, journals and posters as a source of information, mobility, having a personal practitioner, having a healthcare coverage and having an accompaniment for an appointment. Conclusions: Disparities in vaccination coverage exist following a social gradient vulnerability. The public health system and national strategies needs to emphasize the importance to include vulnerable population from the begging on their decision-making.