Grand Prixs and all other full-sized Pontiacs were completely restyled for 1965 featuring more rounded bodylines with Coke-bottle profiles, and a 1 in (25 mm) increase in wheelbase to 121 in (3,100 mm) (for Grand Prix, Catalina, and all Safari station wagons — Bonneville and Star Chief increased proportionally from 123 in (3,100 mm) to 124 in (3,100 mm)).
While other Pontiac coupes received the semi-fastback rooflines shared with other GM divisions, Grand Prixs retained the exclusive squared-off roofline with concave rear window but a bit more rounded than the 1963-64 version.

Interiors were revised with all-new instrument panels featuring a larger dose of walnut trim which now extended to the center console standard with bucket seats, along with a new steering wheel with horn bars replacing the horn ring used in previous years.
The standard bucket seats could be upholstered either in expanded Morrokide vinyl or a new cloth-and-Morrokide trim.
New for 1965 was a no-cost bench seat option with center armrest available with either upholstery choice.

New options included an automatic air conditioning system.
This system, first introduced by Cadillac in 1964, was available in addition to the regular Circ-L-Aire Conditioning.
Hazard flashers were also optional.

Engine offerings were revised for 1965.
The standard four-barrel 389 in³ V8 was uprated to 333 hp (248 kW) with a manual transmission or 325 hp (242 kW) with automatic.
Optional engines included a 389 Tri-Power and 421 four-barrel — both rated at 338 hp (252 kW); a 421 Tri-Power rated at 350 hp (260 kW) and the 421 HO Tri-Power with 376 hp (280 kW).
The standard three-speed and optional four-speed manual transmissions were carried over from 1964, however, a new three-speed Turbo Hydra-matic transmission with torque-converter that was similar in principle to Ford's Cruise-O-Matic and Chrysler's Torqueflite replaced the older three-speed fluid coupling Roto Hydra-matic (along with the four-speed Super Hydra-matic in Bonneville and Star Chief models).
The Turbo Hydra-matic also featured the now-standardized P-R-N-D-S-L shift quadrant pattern in place of the P-N-D-S-L-R setup of previous Hydra-matics.

A 1965 Grand Prix road test was featured in the February, 1965 issue of Motor Trend magazine, much of which was devoted the entire Pontiac lineup receiving M/T "Car of the Year" honors for 1965.
Other Pontiac road tests in that issue included a GTO convertible, Tempest Custom sedan, Catalina Vista hardtop sedan, and Bonneville hardtop coupe.
Grand Prixs and all other full-sized Pontiacs were completely restyled for 1965 featuring more rounded bodylines with Coke-bottle profiles, and a 1 in (25 mm) increase in wheelbase to 121 in (3,100 mm) (for Grand Prix, Catalina, and all Safari station wagons — Bonneville and Star Chief increased proportionally from 123 in (3,100 mm) to 124 in (3,100 mm)). While other Pontiac coupes received the semi-fastback rooflines shared with other GM divisions, Grand Prixs retained the exclusive squared-off roofline with concave rear window but a bit more rounded than the 1963-64 version. 
Interiors were revised with all-new instrument panels featuring a larger dose of walnut trim which now extended to the center console standard with bucket seats, along with a new steering wheel with horn bars replacing the horn ring used in previous years. The standard bucket seats could be upholstered either in expanded Morrokide vinyl or a new cloth-and-Morrokide trim. New for 1965 was a no-cost bench seat option with center armrest available with either upholstery choice.
New options included an automatic air conditioning system. This system, first introduced by Cadillac in 1964, was available in addition to the regular Circ-L-Aire Conditioning. Hazard flashers were also optional.
Engine offerings were revised for 1965. The standard four-barrel 389 in³ V8 was uprated to 333 hp (248 kW) with a manual transmission or 325 hp (242 kW) with automatic. Optional engines included a 389 Tri-Power and 421 four-barrel — both rated at 338 hp (252 kW); a 421 Tri-Power rated at 350 hp (260 kW) and the 421 HO Tri-Power with 376 hp (280 kW). The standard three-speed and optional four-speed manual transmissions were carried over from 1964, however, a new three-speed Turbo Hydra-matic transmission with torque-converter that was similar in principle to Ford's Cruise-O-Matic and Chrysler's Torqueflite replaced the older three-speed fluid coupling Roto Hydra-matic (along with the four-speed Super Hydra-matic in Bonneville and Star Chief models). The Turbo Hydra-matic also featured the now-standardized P-R-N-D-S-L shift quadrant pattern in place of the P-N-D-S-L-R setup of previous Hydra-matics.
A 1965 Grand Prix road test was featured in the February, 1965 issue of Motor Trend magazine, much of which was devoted the entire Pontiac lineup receiving M/T "Car of the Year" honors for 1965. Other Pontiac road tests in that issue included a GTO convertible, Tempest Custom sedan, Catalina Vista hardtop sedan, and Bonneville hardtop coupe.
Pontiac Grand Prix