The invention relates to a method for the synthesis of a branched unsaturated fatty compound, said method comprising the metathesis, in the presence of a metathesis catalyst, of a linear unsaturated fatty compound and a branched olefin. The branched unsaturated fatty compound is used in particular for the production of at least one of the following products: dielectric fluids, specialty surfactants, emulsifiers, frictions agents, antistatic additives, antifogging additives, mould release agents, pigment dispersants, high-performance lubricants, waxes and wax emulsifiers, polymer conversion additives, PVC stabilizing agents, inks, resins, paints, varnishes, solvents, lipsticks, creams for the skin, deodorants, particularly stick deodorants, hair dyes, shampoos and other liquid soaps, shaving foam, laundry detergents, cleaning agents, fabric softeners, and mixtures of same.