<p>There is a scarcity of studies examining the effects of psychological interventions on optimal well-being or flourishing. Two recent randomised controlled trials on the effects of digital self-help positive psychology interventions (PPIs), conducted during and after the Covid-19 pandemic, were analysed post-hoc to address this gap in knowledge. The trials examined the impact of a 6-week gratitude intervention (<i>n</i> = 849) and a 3-week multicomponent PPI (<i>n</i> = 224) in comparison to waitlist control groups in general population samples with moderate distress. In both studies the percentage of flourishing participants in the intervention groups increased to 34% post-intervention and was significantly higher than the proportion of flourishers in the control condition (24% and 16%, respectively), controlling for well-being at baseline. Participants in the gratitude intervention were more than twice as likely (OR = 2.49, 95% CI: 1.67–3.69), and those in the multicomponent PPI more than four times as likely (OR = 4.77, 95% CI: 1.72–13.18), to be flourishing compared to individuals in the control conditions at post-intervention. The results show that digitally delivered positive psychology interventions can support increases in optimal well-being among adults with mild to moderate distress, with effects generally maintained at three-month follow-up. While most participants did not reach full flourishing, these findings suggest that scalable digital PPIs are a feasible approach to promoting optimal population well-being. Further research is needed to confirm effectiveness in more diverse and representative populations.</p>