Digital Twins (DTs) are transforming sustainable development by creating dynamic virtual replicas of physical systems for real-time monitoring, simulation, and intelligent decision- making. This paper integrates four critical pillars—virtual replication, improved decision- making, energy efficiency, and smart infrastructure—to present a unified framework for DT- enabled sustainability. Through a PRISMA systematic review of 55+ studies (2019–2026) and simulated analytical modeling across 100 smart-city nodes, 100 building instances, and 80 buildings with 20 grid zones, the study demonstrates that DTs improve decision accuracy by up to 85%, achieve 20–50% energy savings through modular frameworks, reduce grid transmission losses by 40%, and increase renewable integration to 68% at autonomous intelligence levels. The proposed hierarchical framework integrating IoT edge devices, AI optimization layers, and cloud simulations enables seamless grid-building coordination. Key gaps include limited interoperability, cybersecurity vulnerabilities, and insufficient empirical data from emerging economies. This research contributes to UN SDGs 7, 11, and 12.