A flame-retardant composition includes a crystalline propylene homopolymer or copolymer, a copolymer of ethylene with at least one alpha-olefin having from 3 to 12 carbon atoms, and optionally with a diene, the copolymer of ethylene being characterized by a composition distribution index greater than 45%, the index being defined as a weight percentage of copolymer molecules having an alpha-olefin content within 50% of an average total molar content of alpha-olefin, and natural magnesium hydroxide in amounts such as to impart flame-retardant properties. A related cable with self-extinguishing properties includes a conductor and a flame-retardant coating. The flame-retardant coating includes the flame-retardant composition. A related method for manufacturing a cable having improved mechanical properties and enhanced fire resistance includes the steps of preparing a polymer mixture with flame-retardant properties and extruding the mixture on a conductor optionally pre-coated with an insulating layer, in order to obtain a flame-retardant coating.