Public-private partnerships (PPPs) have become an important option for financing urban rail transit (URT) projects. To ensure the effective operation of URT projects and better serve the public, governments must select suitable operators as part of private-sector consortiums to achieve successful PPP implementations, but they often face a dilemma in choosing between local URT groups and nonlocal operators. In this study, we examine the key factors that determine governments’ operator choices for URT PPP (URT3P) projects with a two-stage approach. A four-dimensional (4D) indicator system containing 20 factors was first developed, and least absolute shrinkage and selection operator (LASSO) regression was applied to analyze one of the largest regional URT data sets in China. Five key factors that significantly influence operator selection are identified, including project operation duration, government-business relationships, private-sector entity organization type, private-sector entity ownership type, and whether the private-sector entity owns an operating firm. This study contributes to the body of knowledge on URT3P project management, and this systematic approach can be used by local governments to select suitable operating partners in similar exploratory contexts.