Background: The aim of this analysis was to calculate the incidence of hepatitis C virus (HCV) reinfection and associated factors among 2 clinical trials of HCV direct-acting antiviral treatment in people with recent injecting drug use or currently receiving opioid agonist therapy (OAT). Methods: Participants who achieved an end-of-treatment response in 2 clinical trials of people with recent injecting drug use or currently receiving OAT (SIMPLIFY and D3FEAT) enrolled between March 2016 and February 2017 in 8 countries were assessed for HCV reinfection, confirmed by viral sequencing. Incidence was calculated using person-time of observation and associated factors were assessed using Cox proportional hazard models. Results: Seventy-three percent of the population at risk of reinfection (n = 177; median age, 48 years; 73% male) reported ongoing injecting drug use. Total follow-up time at risk was 254 person-years (median, 1.8 years; range, 0.2-2.8 years). Eight cases of reinfection were confirmed for an incidence of 3.1/100 person-years (95% confidence interval [CI], 1.6-6.3) overall and 17.9/100 person-years (95% CI, 5.8-55.6) among those who reported sharing needles/syringes. Younger age and needle/syringe sharing were associated with HCV reinfection. Conclusions: These data demonstrate the need for ongoing monitoring and improved strategies to prevent HCV reinfection following successful treatment among people with ongoing injecting drug use to achieve HCV elimination. Clinical Trials Registration: NCT02336139 and NCT02498015.