Composite materials formed of a matrix of fused ceramic grains with single-wall carbon nanotubes dispersed throughout the matrix and a high relative density, notably that achieved by electric field-assisted sintering, demonstrate unusually high electrical conductivity in combination with high-performance mechanical properties including high fracture toughness. This combination of electrical and mechanical properties makes these composites useful as electrical conductors in applications where high-performance materials are needed due to exposure to extreme conditions such as high temperatures and mechanical stresses.