Background <p>In many jurisdictions world-wide, the government agency that manages prisons also provides prison health care services. However, the World Health Organization (WHO) and United Nations (UN) have recommended that health ministries provide prison health care. In Canada, the province of British Columbia (BC) transferred responsibility for correctional health services to the health ministry in accordance with this guidance. The objective of this study was to estimate the association between the transfer in BC and all-cause and overdose mortality within 1 year of release from prison.</p> Methods <p>We used a retrospective cohort study design employing the difference-in-differences (DiD) method to compare mortality among formerly-incarcerated people in the pre- and post-transfer periods against a matched community control group to control for province-wide trends in mortality. The data source was a longitudinal linkage of administrative databases. The DiD effect was estimated with survival time-to-event models.</p> Results <p>In the formerly-incarcerated group (<i>N</i> = 6912), all-cause (3.7% vs 2.6%) and overdose (2.7% vs 1.7%) mortality in the first-year post-release decreased from the pre-transfer period to the post-transfer period, while mortality risk changed little in the community control group (<i>N</i> = 6881) during this time period (all-cause: 0.7% vs 0.9%; overdose: 0.4% vs 0.4%). The transfer was associated with statistically significant reductions in the hazards of all-cause mortality (DiD HR: 0.52, 95% CI: [0.32, 0.83]) and overdose mortality (DiD HR: 0.51, 95% CI: [0.26, 0.99]) in the first-year post-release.</p> Conclusions <p>This study provides empirical evidence in support of WHO and UN guidance and indicates that the delivery of correctional health services by community health authorities may reduce deaths, particularly overdose deaths, among people released from correctional centres.</p>