<p>Over the past three decades, research on sustainable cities has expanded rapidly, encompassing nature–based solutions, sustainability assessment frameworks, smart technologies, and low–carbon policies. However, much of the existing literature focuses on individual concepts or tools, resulting in a fragmented research landscape in which the empirical research context and the long–term structural evolution of sustainable city research lack an integrated empirical examination. This study uses 10,096 journal articles published between 1994 and 2025 and indexed in the Web of Science Core Collection as empirical data. A citation network is constructed, and Main Path Analysis is applied as the core empirical method to systematically reconstruct the knowledge evolution of sustainable city research. Key–route analysis, cluster analysis, and emerging topic analysis are further integrated to identify influential knowledge pathways, research branches, and convergence patterns. The empirical results reveal a clear structural transformation in the field. Early research was dominated by normative discussions on environmental constraints, social justice, and urban development. This was followed by an institutionalization phase in which sustainability indicators and assessment tools translated normative objectives into measurable and governable policy objects. In recent years, research has converged toward a governance–oriented and policy–effect–focused paradigm, treating cities as policy laboratories for low–carbon transitions, causal evaluation, and institutional learning. Overall, this study demonstrates how sustainable city research has evolved from conceptual and normative discourse into a governance–centered, policy–operational empirical research system, highlighting the role of cities as institutional laboratories in contemporary sustainability research.</p>