Gas-insulated switchgear (GIS) and transmission lines (GIL) depend on epoxy spacers to ensure electrical reliability under high-voltage stress. Yet, the limited dielectric strength and thermal tolerance of neat epoxy constrain its long-term applicability. This work investigates Zn/Al layered double hydroxide (LDH) nanoparticles as functional fillers for epoxy insulation. The nanofillers were synthesized by co-precipitation, surface-functionalized for improved compatibility, and incorporated into epoxy at loadings of 1–7 wt%. Structural, thermal, dielectric, and breakdown properties were systematically assessed. The Zn/Al-LDH exhibited a mesoporous nanostructure with high surface area (~98.9 m²/g) and uniform dispersion in the matrix, increasing epoxy structural ordering from 21.1% to 28.9%. Thermal stability improved as the char yield rose from 14% (neat epoxy) to 17.1% at 5 wt%, while the glass transition temperature shifted from 93.5 °C to 109.8 °C, surpassing the IEC 62271-1 limit. Dielectric analysis confirmed stable permittivity, low loss at 50 Hz, and suppressed DC conductivity down to 10⁻¹⁵–10⁻¹² S/cm. Most notably, breakdown strength rose from 30.08 kV/mm in neat epoxy to 37.42 kV/mm at 5 wt%, representing a 24% enhancement and the most reliable statistical profile under Weibull analysis. Beyond this concentration, agglomeration effects reversed the benefits, lowering performance below that of pure epoxy. These findings highlight Zn/Al-LDH/epoxy nanocomposites as a promising class of advanced insulating materials, with optimum performance achieved at 3–5 wt% loading. The combined improvements in dielectric reliability, thermal stability, and breakdown endurance demonstrate their potential for next-generation GIS/GIL applications.