Background and aims: Substance use treatment (SUT) has shown to be effective in reducing self-reported offending; however, the association between SUT completion and criminal justice system (CJS) contact has been underexplored, especially in Latin America. This study aimed to estimate the association between SUT completion status and (1) any subsequent CJS contact and (2) CJS contact leading to imprisonment, at 1, 3 and 5 years post-discharge, in Chile. Design: Retrospective cohort study using multivariable survival analysis based on linked administrative data from 2010 to 2019. Setting: This study took place in Chile, where SUT is available at no cost through Chile's publicly funded health-care, and is provided in outpatient and inpatient modalities in public and private centres. Participants: A total of 70 854 individuals received their first SUT from 2010 to 2019. They were mainly males (76.3%), and their main substance used at admission was cocaine paste (39.2%). Measurements: SUT completion status included completion, late dropout (≥ 3 months) and early dropout (< 3 months). Outcomes were (1) any CJS contact and (2) CJS contact leading to imprisonment after baseline treatment. We estimated the association between treatment completion and CJS contact through flexible parametric Royston−Parmar models while adjusting for several covariates. Findings: Those who completed SUT (27.2%) were less likely to have any CJS contact at 5 years post-SUT compared with those who dropped out late [with a gap of −9.5%, 95% confidence interval (CI) = −8.7, −10.3] and early (−11.2%, 95% CI = −10.1, −12.3). Also, those who completed SUT were less likely to have CJS contact leading to imprisonment at 5 years post-SUT compared with those who dropped out late (−2.6%, 95% CI = −2.2, −3.1) and early (−4.0%, 95% CI = −3.3, −4.6). These differences were also observed at 1 and 3 years post-SUT for each outcome. Conclusions: In Chile, completion of substance use treatment appears to be associated with lower probabilities of both any criminal justice system contact and contact leading to imprisonment.