Under rapid urbanisation and climate change, cities urgently need strategies to enhance resilience and sustainability. Transforming brownfields into green spaces has been widely recognised as a nature-based solution (NbS), yet how to integrate this transformation into urban planning to maximise benefits remains unclear. To address the gap, our study proposes a cross-scale approach for brownfield greening (BG) that links urban-scale prioritisation with site-specific greening interventions. By integrating spatially explicit assessments of ecosystem service (ES) supply, demand and supply-demand balance, the approach identifies not only where BG should occur (where to green), but also how tailored interventions can be implemented within sites (how to green). The proposed approach was tested in Tangshan, a typical resource-exhausted city in China, demonstrating how ES assessments can guide both strategic planning and detailed planning of BG. The findings advance the integration of NbS into spatial planning at multiple levels, offering actionable guidance for policy-makers, urban planners and landscape architects. Beyond the case study, the approach also provides insights into managing land abandonment in shrinking cities worldwide, contributing to more effective and transferable urban greening strategies.