We conducted a prospective cohort study to evaluate intimate partner violence (IPV) as a risk factor for detectable plasma viral load in HIV-positive female sex workers (FSWs) on antiretroviral therapy (ART) in Kenya. IPV in the past year was defined as =1 act of physical, sexual, or emotional violence by the index partner (i.e. boyfriend/husband). The primary outcome was detectable viral load (=180 copies/ml). In-depth interviews and focus groups were included to contextualize results. Analyses included 195 women (570 visits). Unexpectedly, IPV was associated with significantly lower risk of detectable viral load (adjusted relative risk 0.21, 95 % CI 0.05–0.84, p-value = 0.02). Qualitative findings revealed that women valued emotional and financial support from index partners, despite IPV. IPV was not a major barrier to ART adherence. The observed association between IPV and lower risk of detectable viral load in FSWs may be due to unmeasured personal and relationship factors, warranting further research.