The exterior of the GNX reflects the very best of both form and function. The GNX received stylish and functional front fender vents just forward of the doors, rooted in the tradition of the VentiPorts featured on classic post-war Buicks. Special composite fender flares were fitted to the wheel wells to make room for the larger wheels and tires and provide a distinctive styling cue. Goodyear Eagle VR performance tires were mounted on custom-made super lightweight alloy lace wheels with black centers and lug caps, each accentuated by a deep, finely-polished rim. The GNX was the first modern Buick ever to receive 16-inch wheels. The rear wheels are wider than the front with special offsets exclusive to the GNX and can not be interchanged.
All GNX's are black in color with blacked-out trim, and exterior identification is limited to small “GNX” callouts placed on the front radiator grille, rear deck lid, and wheel centers. In keeping with the stealth, understated theme, no other badging or callouts are used on the exterior body. Under the hood, a special turbocharger heat shield features an exclusive “GNX” stamped design, while the custom aluminum rear differential cover is embossed with “GNX.” Decals and assembly information are found on the intercooler, cowl area, and inside driver's door to indicate each vehicle's special build status.