Pre-exposure prophylaxis (PrEP) is an important biomedical human immunodeficiency virus (HIV) prevention tool gaining more popularity among Parisian men who have sex with men (MSM) who engage in transactional sex. This study examines the knowledge of, and willingness to use, different modalities of PrEP among this subgroup. Broadcast advertisements were placed on a geosocial-networking smartphone application with a link to a Web-based survey during three 24-hour periods in October 2016. Modified Poisson regression models were used to assess the association between engagement in transactional sex and preferences for each of these PrEP modalities. A total of 444 respondents were included. About 14% reported engagement in transactional sex. In all, 90% of MSM who engaged in transactional sex were knowledgeable of daily oral PrEP, while 13.3% were knowledgeable about long-acting injectable PrEP or penile or rectal microbicides. They were more likely to be aware of long-acting injectable PrEP (aRR = 2.52, 95% CI = 1.16 to 5.47) and willing to use daily oral PrEP (aRR = 1.48; 95% CI = 1.11 to 1.98) or long-acting injectable PrEP (aRR = 1.40; 95% CI = 1.09 to 1.81) than MSM who had not engaged in transactional sex. Long-acting injectable PrEP may be an important HIV-prevention option for MSM who engage in transactional sex if this modality is proven effective.