Abstract Background Transactional sex is known to be an exposure factor for HIV acquisition among immigrants in France. We analysed the factors associated with the increase in the proportion of transactional sex among African immigrant men and women living in precarious situations in the greater Paris area. Methods Data were collected in the Makasi research project. Participants were recruited in public places based on their precarious situations, they were randomised into two groups (intervention and control) followed during six months between 2019 and 2021. We described the levels of transactional sex at each follow-up time (0, 3, 6 months) and used random-effects logistic regression models to analyse factors associated with the evolution of transactional sex participants. Results The majority of participants were men (76.5% (470/614)) and almost half of them arrived in France in two years prior to inclusion (49.8%). Transactional sex increased in both study groups: at inclusion, 1% of men in the control group and 0% in the intervention group reported having had transactional sex. At the six-month follow-up, 15% and 8% of men in the control and intervention groups respectively reported transactional sex. Among women, 7% in the control group and 8% in the intervention group reported transactional sex at baseline. They were 27% and 24% respectively to report transactional sex at the six-month follow-up in each group. We find that exposure to the intervention liberate the speech about transactional sex, especially among men. Conclusions Our results suggest that the proportion of transactional sex seems to be important among immigrants in precarious situations, especially among men, and that the empowerment intervention facilitated participants’ openness about their sexual activities. These results suggest that the social hardships and structural barriers faced by immigrants in precarious situations limit the effect of HIV prevention interventions in this population. Key messages • Social hardships experienced by immigrants must be addressed to reduce their exposure to HIV. • An empowerment-based outreach intervention facilitated participants’ openness about transactional sex.