Objective: Act-Belong-Commit is the world's first population-wide, community-based mental health promotion campaign. We assessed the associations between baseline indicators of Act-Belong-Commit behavioral domains and wellbeing at 2-year follow-up in a population-based sample of Irish older adults. Methods: Data from 2 waves of the Irish Longitudinal Study on Ageing were analyzed. The sample consisted of 6098 adults. Outcomes were quality of life (QoL), life satisfaction (LS) and self-rated mental health (SRMH). Multivariable regression analyses were conducted. Results: The adjusted model showed that each increase in the number of social/recreational activities (Act) predicted better QoL and SRMH, but the positive association with LS did not reach statistical significance. Both social network integration (Belong) and frequency of participation in social/recreational activities (Commit) significantly promoted QoL, LS, and SRMH. These associations were apparent regardless of baseline common mental disorders. Conclusion: Act-Belong-Commit indicators are shown to promote wellbeing among Irish older adults, providing further support for the campaign's potential.