Prison staff operate in a high stress environment, causing them to be among the highest occupational groups to file mental stress claims, and being a significant contributor to the $105.5m mental health stress claims faced by Australian organisations. Workforce wellbeing intervention programs that use positive psychology principles and target resilience can offer a solution to improve the mental health of prison workforces. This presentation describes a collaborative project between the Department of Correctional Services (DCS) and the South Australian Health and Medical Research Institute (SAHMRI) Wellbeing and Resilience Centre, investigating the effectiveness of a group wellbeing and resilience skills training program in improving subjective wellbeing and psychological distress of corrections staff. The intervention was delivered over a period of 3 years and provided over 750 employees with basic psychological skills to improve mental health outcomes. The PERMA-profiler and Brief Resilience Scale were used as outcome measures. A significant increase in whole-of-organisation wellbeing levels was observed over the duration of the 24-month project and reductions of gross expenditure mental stress claims by 80% and overall sick leave by 12% were observed, leading to $1.6m in savings over a 12-month period; results which demonstrate the impact of a systems-wide wellbeing implementation.