Control of charge-state stability in near-surface quantum defects is critical for nanoscale sensing, yet remains particularly challenging under ultra-high vacuum (UHV), where surface-induced band bending destabilizes the metrologically relevant charge-state. Here, we present a robust and reproducible approach for stabilizing shallowly implanted (< 10 nm deep) nitrogen-vacancy (NV) centers in near-UHV conditions (P = 3 × 10⁻⁹ mbar) based on dielectric interface engineering. Through measurements on individually addressable NV centers, we demonstrate that a TiO2 coating on the diamond suppresses surface-induced electrostatic fields, yielding a 79% increase n NV- population and a 45% enhancement in NV-spin resonance contrast at room temperature. Coherent control measurements further reveal suppressed charge-state conversion dynamics. These results establish dielectric screening as a powerful and reproducible strategy to engineer charge transition energetics of NV centers in scanning-probe-compatible geometries under extreme conditions.