All A-bodies, including the Grand Prix, were redesigned for 1973.
This generation was larger and heavier, due partly to the federally mandated 5 mph (8.0 km/h) crash bumpers.
Although large V8s were still available, performance was on the decline due to another federal standard—a new emissions control system.
The most notable styling feature of this generation was the appearance of the fixed opera window, replacing the previous disappearing rear side glass.
This year's Grand Prix switched from pillarless hardtop design to a pillared "Colonnade" hardtop with frameless door glass as did all GM intermediates in response to proposed federal safety standards regarding roll-over protection that would have ultimately spelled the end of pillarless and convertible bodystyles, a mandate that never materialized.

Front and rear styling of the 1973 Grand Prix turned out be an evolution of the 1971 and 1972 models with a vertical-bar V-nose grille and single headlamps along with the new federally mandated 5 mph (8 km/h) front bumper.
The rear featured a revised boattail-like trim with square-taillights above the bumper.

Inside, a new instrument panel continued the wraparound cockpit theme of previous models with new African Crossfire Mahogany facing on the dashboard, console and door panels, which was "real" wood in contrast with the simulated woodgrain material found in most car interiors during that time.
The Strato bucket seats were completely new with higher seatbacks and integrated headrests in Morrokide or scivvy cloth trims, and optional recliners and adjustable lumbar support, with a notchback bench seat offered as a no-cost option.

The standard drivetrain consisted of the four-barrel 400 cu in (6.6 L) V8 rated at 230 hp (170 kW) and the Turbo Hydra-Matic transmission.
Also standard were power steering and power brakes.
A four-barrel 455 cu in (7.5 L) was optional and included with the "SJ" option that also added a rally gauge cluster and a radial tuned suspension with front and rear sway bars, Pliacell shock absorbers, and radial-ply tires.

Although the Third Generation Grand Prix was indeed bulkier and heavier than its predecessor, handling was good for a large car, due to improvements in suspension design.
The introduction of radial-ply tires was also a boon for handling.
GM's "A" body cars' front suspensions were based on the Chevrolet Camaro and Pontiac Firebird during this production run.

Grand Prix production set a new record of over 150,000 units, despite intense competition from a similar restyled Chevy Monte Carlo, and "near" personal luxury coupes such as Buick's all-new Century Regal and Oldsmobile's Cutlass Supreme — both of whose styling and appointments were very similar to the GP and Monte Carlo, and even shared the same squared-off formal roofline with opera windows - but used the standard A-body coupe body and 112 in (2,800 mm) wheelbase shared with lower-priced models.
The success of the GP (and Monte Carlo) led to direct responses from Ford Motor Company the following year with a larger  Ford Elite and Mercury Cougar, which were followed by Chrysler entries in 1975, the Dodge Charger and Chrysler Cordoba.
All A-bodies, including the Grand Prix, were redesigned for 1973. This generation was larger and heavier, due partly to the federally mandated 5 mph (8.0 km/h) crash bumpers. Although large V8s were still available, performance was on the decline due to another federal standard—a new emissions control system. The most notable styling feature of this generation was the appearance of the fixed opera window, replacing the previous disappearing rear side glass. This year's Grand Prix switched from pillarless hardtop design to a pillared "Colonnade" hardtop with frameless door glass as did all GM intermediates in response to proposed federal safety standards regarding roll-over protection that would have ultimately spelled the end of pillarless and convertible bodystyles, a mandate that never materialized.
Front and rear styling of the 1973 Grand Prix turned out be an evolution of the 1971 and 1972 models with a vertical-bar V-nose grille and single headlamps along with the new federally mandated 5 mph (8 km/h) front bumper. The rear featured a revised boattail-like trim with square-taillights above the bumper.
Inside, a new instrument panel continued the wraparound cockpit theme of previous models with new African Crossfire Mahogany facing on the dashboard, console and door panels, which was "real" wood in contrast with the simulated woodgrain material found in most car interiors during that time. The Strato bucket seats were completely new with higher seatbacks and integrated headrests in Morrokide or scivvy cloth trims, and optional recliners and adjustable lumbar support, with a notchback bench seat offered as a no-cost option.
The standard drivetrain consisted of the four-barrel 400 cu in (6.6 L) V8 rated at 230 hp (170 kW) and the Turbo Hydra-Matic transmission. Also standard were power steering and power brakes. A four-barrel 455 cu in (7.5 L) was optional and included with the "SJ" option that also added a rally gauge cluster and a radial tuned suspension with front and rear sway bars, Pliacell shock absorbers, and radial-ply tires.
Although the Third Generation Grand Prix was indeed bulkier and heavier than its predecessor, handling was good for a large car, due to improvements in suspension design. The introduction of radial-ply tires was also a boon for handling. GM's "A" body cars' front suspensions were based on the Chevrolet Camaro and Pontiac Firebird during this production run.
Grand Prix production set a new record of over 150,000 units, despite intense competition from a similar restyled Chevy Monte Carlo, and "near" personal luxury coupes such as Buick's all-new Century Regal and Oldsmobile's Cutlass Supreme — both of whose styling and appointments were very similar to the GP and Monte Carlo, and even shared the same squared-off formal roofline with opera windows - but used the standard A-body coupe body and 112 in (2,800 mm) wheelbase shared with lower-priced models. The success of the GP (and Monte Carlo) led to direct responses from Ford Motor Company the following year with a larger  Ford Elite and Mercury Cougar, which were followed by Chrysler entries in 1975, the Dodge Charger and Chrysler Cordoba.
Pontiac Grand Prix