Authors: 1. Hemangi Singh, Tata Institute of Social Sciences 2. Manoj Yellaiah Vallam, Amrita Vishwa Vidyapeetham, Mysuru Campus 3. Shrawani Ganesh Bokshe, KDK College of Engineering 4. Pratishtha, Chandigarh College of Engineering and Technology 5. Saqeef Bayezid Ahsan, University of Dhaka, Bangladesh 6. Aruhi Jain, JSS Science and Technology University 7. Shaik Sameeruddin, Vignana Bharathi Institute of Technology 8. McDonald Julius, Lilongwe University of Agriculture and Natural Resources, Malawi, Africa 9. Asfia Hasan, Jamia Millia Islamia Abstract Rapid urbanization, population growth, and inadequate environmental governance have intensified ecological degradation across cities in the Global South, particularly through the erosion of urban green spaces and the collapse of functional waste management systems. This study examines the intersecting roles of urban green infrastructure and solid waste governance in sustaining ecosystem health, with a focus on India, Bangladesh, and Nigeria as representative developing-nation contexts, benchmarked against European nations, notably Germany, Sweden, and the Netherlands. Employing a qualitative comparative methodology, the study draws on peer reviewed literature, government policy documents, and international organization reports to conduct thematic and comparative policy analyses across four dimensions: urban green space distribution, solid waste management systems, public health and environmental inequality, and governance effectiveness. Findings reveal that urban green spaces deliver critical ecosystem services, including air purification, urban heat island mitigation, and biodiversity conservation, while simultaneously supporting physical and mental well-being among urban populations. Escalating waste generation in cities such as Lagos, Dhaka, and Mumbai overwhelms underfunded collection and disposal systems, generating severe environmental pollution, waterborne disease burdens, and disproportionate health risks in low-income communities. Comparative analysis confirms that European cities achieve superior sustainability outcomes through binding regulatory frameworks, integrated green-waste urban planning, advanced recycling and waste-to-energy technologies, and structural advantages largely absent in developing-country governance contexts. The study concludes that urban ecosystem sustainability cannot be achieved through isolated interventions; it requires the deliberate integration of green infrastructure planning, equitable waste governance, and strengthened institutional accountability. Policy recommendations include enforceable urban green space mandates, formalization of informal waste economies, increased environmental budget allocations, and community-centred governance frameworks. This research contributes a cross-regional comparative perspective to the urban sustainability literature and provides evidence-based direction for policymakers in rapidly urbanizing nations. Keywords: Urban green spaces; solid waste management; ecosystem sustainability; environmental governance; urbanization; developing countries; comparative urban policy.