Aim An assertive case management intervention program, ACTION-J, proved effective for preventing suicide attempters from reattempting suicide within 6 months. The ACTION-J randomized trial was conducted as part of the “National Strategic Research Projects.” The program has been covered by the national medical payment system of Japan since 2016. The aim of the Post-ACTION-J Study (PACS) was to examine the current implementation status of assertive case management in a real-world clinical setting. Methods PACS was a prospective, multicenter registry cohort study. The participants were suicide attempters admitted to the emergency departments of 10 participating medical facilities from October 2016 to September 2018. The assertive case management intervention developed by the ACTION-J Study was offered to all patients, and the primary outcome was the duration and frequency of use of the intervention at 6 months. Results A total of 1159 patients were admitted to emergency departments after a suicide attempt during the study period, 144 of whom were included in our analysis. The proportion of participants who received the intervention for 6 months was 72.2% (104/144), and 63.9% (92/144) of the patients completed ≥7 case management interviews within 6 months. Conclusion The findings of this study indicate successful implementation of an assertive case management intervention program based on the ACTION-J Study in a real-world clinical setting, following its integration with the national medical payment scheme in Japan. The study provided the useful information that could improve the implementation of assertive case management interventions in future.