Permittivity modulation in nonlocal metasurfaces provides an effective route for unlocking radiative coupling of symmetry-protected bound states in the continuum (BICs), enabling unprecedented dynamic control over resonant light-matter interactions. Here, we present a periodically poled lithium niobate metasurface platform that leverages spatially antisymmetric electro-optic responses induced by the Pockels effect to achieve continuous control of radiative coupling. Distinctively, the electro-optic asymmetry introduces an independent and continuously tunable perturbation channel, enabling postfabrication control of the radiative coupling. By interfering with the radiation amplitude induced by unintended structural asymmetry, it enables compensation of geometry-induced radiation leakage to a large extent and thereby restores high-$Q$ resonances. Concurrently, the domain-engineered architecture intrinsically embeds nonlinear optical functionality, operating as a tunable ${\chi }^{\left(2\right)}$ grating that enables large-angle ($71.4^{\circ }$) second-harmonic generation with electrically controlled emission. We demonstrate high nonlinear switching contrast exceeding 22 dB under moderate electric fields ($\le 20\mathrm{V}/\mu \mathrm{m}$), bridging high-$Q$ resonance engineering with nonlinear photonics to provide a unified platform for next-generation on-chip optical switches, dynamic filters, and frequency converters.

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• Dielectric properties
• Metasurfaces
• Nonlinear optics