AbstractBackground & AimsPeople who inject drugs (PWID) experience high incarceration rates which are associated with increased hepatitis C virus (HCV) transmission risk. We assess the importance of prison‐based interventions for achieving HCV elimination among PWID in New South Wales (NSW), Australia.MethodsA model of incarceration and HCV transmission among PWID was calibrated in a Bayesian framework to epidemiological and incarceration data from NSW, incorporating elevated HCV acquisition risk among recently released PWID. We projected the contribution of differences in transmission risk during/following incarceration to HCV transmission over 2020–2029. We estimated the past and potential future impact of prison‐based opioid agonist therapy (OAT; ~33% coverage) and HCV treatment (1500 treatments in 2019 with 32.9%–83.3% among PWID) on HCV transmission. We estimated the time until HCV incidence reduces by 80% (WHO elimination target) compared to 2016 levels with or without prison‐based interventions.ResultsOver 2020–2029, incarceration will contribute 23.0% (17.9–30.5) of new HCV infections. If prison‐based interventions had not been implemented since 2010, HCV incidence in 2020 would have been 29.7% (95% credibility interval: 22.4–36.1) higher. If current prison and community HCV treatment rates continue, there is an 98.8% probability that elimination targets will be achieved by 2030, with this decreasing to 10.1% without current prison‐based interventions.ConclusionsExisting prison‐based interventions in NSW are critical components of strategies to reduce HCV incidence among PWID. Prison‐based interventions are likely to be pivotal for achieving HCV elimination targets among PWID by 2030.