Tensioner for an accessory drive of a motor vehicle each have a support element adapted to be fixed on an electric machine, an intermediate element carried by the support element and rotating with respect thereto about a first fixed axis, a rigid tensioner element rotating with respect to the intermediate element about a second axis parallel to the first axis, a pair of tensioner pulleys carried by the tensioner element and adapted to cooperate with respective branches of an endless drive element of the drive positioned on opposite sides with respect to the electric machine, and a spring acting between the support element and the intermediate element to push the tensioner pulleys into contact with the endless drive element.