As growth-driven health gains in maturing cities become uneven, a paradigm shift toward “Health in All Policies” seeks to align urban development with reciprocal health co-benefits. Urban planning increasingly frames the ecological environment as a lever for health equity, yet its implications for metabolic health remain poorly characterised. Integrating satellite-derived remote-sensing ecological index (RSEI) data with longitudinal information from 315,109 UK urban participants, we examined associations between urban ecological quality and incident type 2 diabetes (T2D). Cox proportional hazards models estimated hazard ratios (HRs) across RSEI categories, with interaction tests for age, sex, and genetic susceptibility, and stratified analyses by T2D phenotype, socioeconomic status (SES), and geographic region. The results demonstrated that improved ecological quality was associated with a stepwise reduction in T2D risk, with HRs of 0.86 (95% CI: 0.82–0.91) and 0.77 (0.72–0.82) for moderate and high RSEI levels, respectively. This protective association was markedly stronger among individuals with lower SES (HR: 0.78, 95% CI: 0.71–0.86) than among higher-status counterparts (0.89, 0.74–1.08), highlighting the equigenic potential of urban ecological environments to attenuate socioeconomic health disparities. Risk reductions were also observed among older adults, individuals with lower genetic susceptibility, and residents of Northern and Midlands England. Synthesising these findings, we propose an urban-ecological cascade framework delineating hierarchical pathways linking urban planning to metabolic health. Urban ecological environments thus emerge not merely as biophysical attributes but as instruments of spatial justice, underscoring the need to embed ecological performance into urban governance to create resilient and health-generating cities.