Rapid urbanization of the human population and the escalating threat of climate change are the main global crises of the 21st century. When cities densify to accommodate the growth, they face critical shortage of urban space and intense competition between gray infrastructure, ecological preservation, and the urgent need for renewable energy generation, calling for effective urban planning as well as management. Traditionally, urban planning operates in isolated departments without cooperation; they simply separate nature into parks, energy into peripheral power plants, and water into underground pipes, leading to more and more vigorous competition for space utilization. This perspective argues that such a fragmented approach is no longer viable, while a new paradigm of spatial synergy integrating blue–green infrastructure (BGI) and renewable energy sources (RES) possesses encouraging potential and is gaining increasing attention. After discussing the mechanics, the planning methodologies, and the operational frameworks of the spatial synergy, the critical challenges and specific barriers in the synergistic integration are summarized in the dimensions of spatial planning, operation and techniques, socio-economics and governance, and the interconnected pathways, spanning good planning, honest financing, and inclusive governance are proposed to provide a clear roadmap for achieving tangible sustainable urbanism.