Click chemistry type reactions between polyethylene-based copolymers are a promising and by-product free alternative to peroxide crosslinking of low-density polyethylene, which is widely used as an insulation material for high-voltage power cables. Here, the impact of thermal ageing on the long-term stability of the thermo-mechanical and dielectric properties of a copolymer blend is evaluated that can be cured through a by-product free reaction between the epoxy and carboxylic acid functional groups attached to the polyethylene backbone. It is observed that ageing at 90 °C in air for up to 2500 h does not affect the direct current (DC) electrical conductivity of about 3 × 10⁻¹⁴ S m⁻¹, provided that a suitable antioxidant is added that prevents the thermo-oxidative degradation of the polyethylene backbone. Furthermore, the material maintains its thermo-mechanical properties upon ageing such as a high ductility at room temperature and a stiffness of about 1 MPa above the melting temperature of polyethylene. Evidently, the use of click chemistry type reactions is a promising strategy for the design of new high-voltage insulation materials that can be cured without the formation of by-products.