Ecological-collective-flourishing (e-co-flourishing) describes the interconnected flourishing of human and non-human natural entities. Despite existing conceptual frameworks, translation into practice remains inadequate owing to insufficient synthesis of empirically tested mechanisms driving change across human and ecological systems. We conducted an umbrella review of systematic reviews examining mechanisms at the e-co-flourishing interface. Searches of seven databases and four grey literature sources identified nine eligible reviews. Evidence supported several cross-domain mechanisms, including psychological (eg, attention restoration and reduced stress), social (eg, cohesion and contact), physical (eg, activity), and environmental pathways (eg, reduced stressors and enhanced environmental quality). Psychological mechanisms showed the most consistent support, whereas evidence for other mechanism domains was mixed. Evidence for causality was weak and largely derived from cross-sectional and qualitative studies, and no reviews examined reciprocal mechanisms influencing both human and non-human flourishing. Future research should prioritise rigorous designs, theory-driven testing, and replication to strengthen evidence for equitable and sustainable e-co-flourishing pathways.