Smartphones are revolutionizing approaches to wellbeing investment. Those seeking greater happiness can engage with thousands of downloadable self-help applications instantly, yet the effectiveness of these strategies remains unknown. As wellbeing can be significantly enhanced by positive psychological interventions, the present investigation explored the viability of delivering this content in application format to the happiness seekers it is targeting. A smartphone-based randomized-controlled trial was conducted with a self-selecting pool, randomly assigned to engage with an empirically based mindfulness intervention (n = 57) or a placebo intervention (n = 64) for ten days. The study explored the feasibility of smartphone intervention delivery, the importance of empirically based content and the extent to which subjective experience ratings related to wellbeing gains. Results showed engagement with the mindfulness application lead to significant gains in positive affect with a medium effect size and reduced depressive symptoms with a small effect size. No significant gains were observed in the control condition. Ratings of task enjoyment were positively associated with wellbeing gains. A positive trend was observed between task ease and gains made. Findings support the viability of smartphone-based interventions to significantly enhance wellbeing, underscoring the importance of application content and person-activity fit. This investigation presents implications for happiness seeking strategies in the real world whilst showcasing a dynamic method of intervention delivery that can benefit future research and practice. The greatest mission of positive psychology is to enhance global flourishing; the prevalence of smartphones and the potential of interventions may play a vital role.