Psychosis is a known risk factor for offending behavior, but little is known about the association between clinical contact with mental health services after an offense and reoffending. To examine the association between early contact with mental health services and reoffending after an index offense in individuals with psychosis. In this cohort study, individuals diagnosed with psychosis before their index offense from July 1, 2001, to December 31, 2012, and who received a noncustodial sentence were identified by linking health and offending databases in New South Wales, Australia. The incidence of and risk factors for reoffending and time to reoffending within 2 years from the index offense were examined using Cox proportional hazards regression and Kaplan-Meier survival estimates. Specifically, the association between contact with mental health services within 30 days after an offense and reoffending was examined. Data were analyzed from July 1, 2019, to March 5, 2020. Hospital admission, emergency department presentation, and contact with community mental health services associated with psychosis. Reoffending within 2 years of the index offense was compared in individuals with and without clinical contact with mental health services within 30 days after an offense, with adjustment for potential confounders. Of the 7030 offenders with psychosis (4933 male [70.2%]; median age at the index offense, 34 [interquartile range, 26-42] years), 2605 (37.1%) had clinical contact with mental health services within 30 days after the index offense. The risk of reoffending was significantly lower in those with vs without clinical contact (adjusted hazard ratio [AHR], 0.83; 95% CI, 0.76-0.91). The risk of reoffending was 30% less in male offenders with 5 or more clinical contacts compared with male offenders with no clinical contact (AHR, 0.71; 95% CI, 0.59-0.84). Reoffending in both male and female offenders was associated with younger age (eg, AHR for male offenders aged <18 years, 3.31 [95% CI, 2.39-4.59]; AHR for female offenders aged <18 years, 2.60 [95% CI, 1.69-3.99]) and offending history (eg, AHR for male offenders with ≥4 prior offenses, 2.28 [95% CI, 1.98-2.64]; AHR for female offenders with ≥4 prior offenses, 2.22 [95% CI, 1.67-2.96]). In this cohort, early and frequent clinical contact with mental health services after an offense in individuals with psychosis was associated with reduced risk of reoffending in this group. More support may be needed for early treatment of those with serious mental illness who are at risk of reoffending.