This paper presents a novel adaptive charging strategy for a three-phase bidirectional on-board electric vehicle (EV) charger, en-abling seamless Grid-to-Vehicle (G2V) and Vehicle-to-Grid (V2G) operations while enhancing battery longevity and grid compatibil-ity. The system integrates real-time battery state-of-charge (SOC) and temperature feedback with a predictive first-order thermal model to dynamically adjust charging parameters, mitigating degradation. Featuring a three-phase LCL filter, an AC-DC convert-er, and a buck-boost DC-DC converter, the charger employs Proportional-Integral (PI) control for the AC-DC converter and an Adaptive controller for the DC-DC converter to achieve low total harmonic distortion (THD) of 1.33% (G2V) and 1.7% (V2G), 98.3% efficiency, and a 30% reduction in charging time (5 hours for 20%–80% SOC) compared to conventional methods. MATLAB/Simulink simulations confirm robust performance under sensitivity analysis, demonstrating stability. The system’s unified control framework, combining SOC-based mode switching, thermal derating, and harmonic suppression, outperforms existing methods, offering a scalable solution for smart grid integration and sustainable EV charging infrastructure.