This study examines how Green Leadership drives Sustainable Business Performance through the joint mediation of green organizational identity (GOI) and green human resource management policies (GHP), grounded in the resource-based view. Three gaps motivate this research: the undertheorized joint mediation mechanisms, the unmodeled symbiotic reinforcement loop between the GOI and GHP, and the inferential limitations of conventional bootstrapping. A Monte Carlo simulation-based PLS-SEM framework (K = 10,000 iterations) was applied to data from 218 managers across diverse Vietnamese industries. The results confirmed a significant direct effect of Green Leadership on Business Performance (beta = 0.208, 95% MC-CI [0.107, 0.315]), with the total indirect effect through both mediators substantially larger (beta = 0.436; VAF = 67.7%). A strong symbiotic GOI-to-GHP path was confirmed (beta = 0.490, 95% MC-CI [0.392, 0.581]), positioning collective green identity and green human capital as co-evolving VRIN resources that jointly drive sustainable competitive advantages.