Once again an option package for the LeMans, the 1973 GTO shared the reskinned A-body with its "Colonnade" hardtop styling, which eliminated true hardtop design because of the addition of a roof pillar but retention of frameless doorwork. Rear side windows were now of a fixed design that could not be opened and in a trianglar shape. New federal laws for 1973 demanded front bumpers capable of withstanding 5 mile per hour impacts with no damage to the body (5 mph rear bumpers became standard in 1974). The result was the use of prominent and heavy chrome bumpers front and rear. The overall styling of the 1973 Pontiac A-body intermediates (LeMans, Luxury LeMans, GTO and Grand Am) was generally not well received by the car buying public.

In contrast, the Pontiac Grand Prix and Chevrolet Monte Carlo, which were also derived from the intermediate A-body, were much better received because of their squared-off styling and formal rooflines with vertical windows. Pontiac's sister division, Oldsmobile, received better reviews from the automotive press and the car-buying public with the similar-bodied Cutlass.

Again, the 1973 GTO option was offered on two models including the base LeMans coupe or the LeMans Sport Coupe. The base LeMans coupe featured a cloth-and-vinyl or all-vinyl bench seat while the more lavish LeMans Sport Coupe had all-vinyl interiors with Strato bucket seats or a notchback bench seat with folding armrest. The LeMans Sport Coupe also had louvered rear side windows from the Grand Am in place of the standard triangular windows of the base LeMans.

The standard 400 CID V8 in the 1973 GTO was further reduced in compression to 8.0:1, dropping it to 230 hp. The 400 engine was available with any of the three transmissions including the standard three-speed manual, or optional four-speed or Turbo Hydra-Matic. The 455 CID V8 remained optional but was dropped to 250 hp and available only with the Turbo Hydra-Matic transmission. The 455 HO engine did not reappear, but GM initially announced the availability of a Super Duty 455 engine (shared with the contemporary Pontiac Trans Am SD455), and several such cars were made available for testing, impressing reviewers with their power and flexibility. Nevertheless, the Super Duty was never actually offered for public sale in the GTO. Also, eight (8) 455SD Grand Ams were also built for testing, and eventually all were destroyed as well.

Sales dropped to 4,806, thanks in part to competition from the new Grand Am and the lack of promotion for the GTO. By the end of the model year an emerging energy crisis quashed consumer interest in muscle cars.