Wilson disease is a rare autosomal-recessive disorder caused by mutations in ATPase copper-transporting-β (ATP7B), resulting in excessive copper accumulation in the liver. Existing copper chelators exert adverse effects and are ineffective in patients with advanced liver disease. Here, Lichtmannegger et al. report the therapeutic potential of methanobactin (MB), a peptide produced by Methylosinus trichosporium OB3b, which has a high copper affinity. In Atp7b-deficient rats, short-term MB treatment markedly reduced total liver copper levels to a greater extent than existing copper chelaters, rescuing rats from severe acute liver failure, without signs of toxicity.