A motor vehicle exhaust line includes a hot pipe, and a cold pipe for exhaust gases. A mechanical decoupling element connects a downstream end of the hot pipe to an upstream end of the cold pipe. The exhaust line also includes a nitrogen oxide treatment device and an injector intended to reinject a reagent into, or to produce a reagent in the exhaust line upstream of the nitrogen oxide treatment device. The exhaust line includes a mixer intended to mix the exhaust gases and the reagent injected or produced by the injector. The mixer is positioned upstream of the nitrogen oxide treatment device. The nitrogen oxide treatment device is disposed in the cold pipe downstream of the mechanical decoupling element. The injector and the mixer form an assembly connected directly to the mechanical decoupling element.