Objective The present study investigated the efficacy of a 6‐hour self‐directed workbook adapted from the REACH Forgiveness intervention. Method Undergraduates (N = 41) were randomly assigned to either an immediate treatment or waitlist control condition. Participants were assessed across 3 time periods using a variety of forgiveness outcome measures. Results The 6‐hour workbook intervention increased forgiveness, as indicated by positive changes in participants’ forgiveness ratings that differed by condition. In addition, benchmarking analysis showed that the self‐directed workbook intervention is at least as efficacious as the delivery of the REACH Forgiveness model via group therapy. Conclusion A self‐directed workbook intervention adapted from the REACH Forgiveness intervention provides an adjunct to traditional psychotherapy that could assist the mental health community to manage the burden of unforgiveness among victims of interpersonal harm.