Background The World Health Organization recommends pre-exposure prophylaxis (PrEP) for all populations at substantial risk of HIV infection. However, at-risk women very rarely use PrEP in France—this represents a critical issue among migrant women sex workers (MWSWs). Previous studies on PrEP use among women sex workers or migrants focused on individual or social determinants of motivation. However, operational studies in real-word settings using a holistic population approach to maximize PrEP adherence among MWSWs are lacking. Objective FASSETS (ie, “Favoriser l’Accès à la Santé Sexuelle des Travailleuses du Sexe”; English: “facilitate the access to Sexual Health in women sex workers”) is a participative, multilevel, mixed methods study aiming to improve global knowledge of and access to sexual health care and PrEP among MWSWs through targeted empowerment strategies. Methods This study comprises several phases: (1) phase 1: an initial qualitative study combining semistructured interviews, informal interviews, and participative observations will be performed among MWSWs, local community nongovernmental organizations, and institutions providing sexual reproductive health services to identify the determinants of PrEP access among MWSWs and for respondent-driven sampling (RDS); (2) phase 2: the size of the hidden MWSW population is estimated in Marseille through capture-recapture (the RDS survey will serve as “recapture”); (3) phase 3: a longitudinal cohort will be formed through RDS to represent the MWSW population with a goal of 150 inclusions—this cohort will be followed up for 12 months, and sequential questionnaires exploring medical history; knowledge of sexual health, HIV, and sexually transmitted infections; migration route; and current living conditions will be administered at inclusion (month 0) and months 3, 6, and 12 to measure the following interventional phase’s outcomes; and (4) phase 4: an interventional study with community empowerment actions about sexual health and PrEP will be conducted with community health workers; standardized questionnaires and semistructured interviews, observations, and focus groups will highlight MWSWs’ experiences with empowerment resources, concerns about sexual health, and especially PrEP use or uptake, and we will evaluate whether and how community-adapted empowerment actions conducted by community health workers are effective in increasing access to sexual health, prevention and screening of sexually transmitted infections, and PrEP knowledge and access among MWSWs. Results Recruitment commenced on March 1, 2022. We estimate the follow-up period to end on September 30, 2023. Conclusions This multiphase study will provide robust evidence about the magnitude of the MWSW population in Marseille (the second largest town in France) and their current conditions of living, access to and knowledge of sexual health, and PrEP access. Using a mixed methods analysis, we will investigate whether individual and collective community health empowerment approaches can facilitate access to PrEP and its initiation, use, and adherence in this vulnerable population. International Registered Report Identifier (IRRID) DERR1-10.2196/42844