HIV prevalence among cisgender female sex workers (FSW) and/or women who use drugs (WWUD) is substantially higher compared to similarly aged women. Consistent with PRISMA guidelines, we conducted the first systematic review on the pre-exposure prophylaxis (PrEP) continuum among FSW and/or WWUD, searching PubMed, Embase, CINAHL, PsycInfo, and Sociological Abstracts. Eligibility criteria included: reporting a PrEP related result among FSW and/or WWUD aged 18 + ; peer-reviewed; and published in English between 2012 and 2018. Our search identified 1365 studies; 26 met eligibility requirements, across the following groups: FSW (n = 14), WWUD (n = 9) and FSW-WWUD (n = 3). Studies report on at least one PrEP outcome: awareness (n = 12), acceptability (n = 16), uptake (n = 4), and adherence (n = 8). Specific barriers span individual and structural levels and include challenges to daily adherence, cost, and stigma. Combining health services and long-acting PrEP formulas may facilitate better PrEP uptake and adherence. The limited number of studies indicates a need for more research.