A resin composition, containing an ethylene-vinyl acetate copolymer (A); and 15 to 30 mass parts of a bromine-based flame retardant (B), 5 to 15 mass parts of antimony trioxide (C), 6 to 12 mass parts of a benzimidazole-based aging retardant (D), 2 to 4 mass parts of a phenol-based aging retardant (E), 2 to 4 mass parts of a thioether-based aging retardant (F), 0.5 to 2 mass parts of a copper inhibitor (G), and 3 to 6 mass parts of a crosslinking aid (H), with respect to 90 to 100 mass parts of the ethylene-vinyl acetate copolymer (A); a vehicle wire harness; and, a method of producing a vehicle wire harness.