Somewhat inevitably, the mechanics were based on the Renault R312. In fact, the new bus used the whole of the rear end from the R312, from the rear axle backwards. This was married to a new front end and bodywork designed by Heuliez to form the new bus. Initially both Renault and Heuliez marketed the new machine, Renault-badged buses being called the Renault Heuliez Citybus and those sold through Heuliez being known as the Heuliez Access'bus GX317. The bus went into full production in 1995. As the first all-French low-floor bus, the GX317 was eagerly awaited by operators and quickly appeared in many large fleets. Even those fleets that had found the R312's mechanical layout a bit daunting (such as Toulouse) were convinced by the benefits of the low floor and began ordering the new bus. The Renault-badged version was however to be short lived, and all GX317s now being produced are badged as Heuliez.

Despite the Heuliez-designed bodywork, the GX317's parentage is clear from its mechanical layout. The low floor and deep windows result in the bus having a rather heavy-looking roofline. This is accentuated by a large, square destination display and some rather narrow headlights. Since the rear end of the bus is taken directly from the R312, it looks very similar, however Heuliez did redesign the engine cover. Inside the bus, the floor is flat from the front to just behind the central exit, and then ramps up to clear the rear axle. Both two-door and three-door GX317s have been produced. In the three-door version, there's usually a single step at the rear exit, however on the most recent versions the opportunity has been seized to eliminate this by using a new rear axle design.

At the time of introduction of the GX317, Volvo also held a large interest in the Heuliez company. Before long, Heuliez were also building GX317-style bodies on Volvo B10L chassis. These buses are marketed as the Heuliez GX217, and look very similar to the GX317 from most angles (although the rear end layout is completely different as the Volvo underframe has a longitudinal-mounted engine). An articulated version of the GX217 was also available, based on the Volvo B10LA chassis and marketed as the GX417. Production of the GX217 and GX417 finished in 2001 when Volvo ceased to be a shareholder in Heuliez.

Liquid Petroleum Gas and Compressed Natural Gas-powered versions of the GX317 have followed the more conventional diesel-powered machines. These have gas tanks mounted on the roof and can now be found in a number of French provincial towns as well as in the capital.