The Tempest line received another facelift for the 1970 model year. Hidden headlights were deleted in favor of four exposed round headlamps outboard of narrower grille openings. The nose retained the protruding vertical prow theme, although it was less prominent. While the standard Tempest and LeMans had chrome grilles, the GTO retained the Endura urethane cover around the headlamps and grille.

The suspension was upgraded with the addition of a rear anti-roll bar, essentially the same bar as used on the Oldsmobile 442 and Buick Gran Sport. The front anti-roll bar was slightly stiffer. The result was a useful reduction in body lean in turns and a modest reduction of understeer.

Another handling-related improvement was optional variable-ratio power steering. Rather than a fixed ratio of 17.5:1, requiring four turns lock-to-lock, the new system varied its ratio from 14.6:1 to 18.9:1, needing 3.5 turns lock-to-lock. Turning diameter was reduced from 40.9 feet to 37.4 feet.

The base engine was unchanged for 1970, but the low-compression economy engine was deleted and the Ram Air III and Ram Air IV remained available, although the latter was now a special-order option.

A new option was Pontiac's 455 engine, available now that GM had rescinded its earlier ban on intermediates with engines larger than 400. The 455, a long-stroke engine taken from the full-size Pontiac Bonneville line, was only moderately stronger than the base 400 and actually less powerful than the Ram Air III. The 455 was rated at 360 hp at 4,300 rpm. Its advantage was torque: 500 lb·ft at 2,700 rpm. A functional Ram Air scoop was available, but even so equipped, a stock 455 was less powerful than the Ram Air III. Car and Driver tested a heavily optioned 455, with a four-speed transmission and 3.31 axle and recorded a quarter mile time of 15.0 seconds with a trap speed of 96.5 mph. Car Life's Turbo-Hydramatic 455, with a 3.35 rear differential, clocked 14.76 seconds at 95.94 mph, with identical 6.6 second 0-60 mph acceleration. Both were about 3 mph slower than a Ram Air III 400 four-speed, although considerably less temperamental: the Ram Air engine idled roughly and was difficult to drive at low speeds. The smaller displacement engine recorded less than 9 mpg of gasoline, compared to 10-11 mpg for the 455.

A new and short-lived option for 1970 was the Vacuum Operated Exhaust (VOE), which was vacuum actuated via an underdash lever marked "EXHAUST." The VOE was designed to reduce exhaust backpressure to increase power and performance, but it also substantially increased exhaust noise. The VOE option was offered from November 1969 to January 1970. Pontiac management was ordered to cancel the VOE option by GM's upper management following a TV commercial for the GTO that aired during Super Bowl IV on CBS January 11, 1970. In that commercial, entitled "The Humbler," which was broadcast only that one time, a young man pulled up in a new GTO to a drive-in restaurant with dramatic music and exhaust noise in the background, pulling the "EXHAUST" knob to activate the VOE and then left the drive-in to do some street racing. That particular commercial was also cancelled by order of GM management. Approximately (134) 1970 GTOs were factory built with this rare option, all were "YS" 400ci 350hp/Automatics. This particular GTO in the commercial was Palladium Silver with a Black bucket interior. It was unusual in several respects as it also had the under-dash "RAM AIR" knob just to the right of the VOE knob, and it sported '69 JUDGE stripes, as a few very-early '70 GTOs could be ordered with. It also had a remote mirror, Rally II wheels, A/C, Hood Tach, and a new-for-1970 Formula steering wheel. A few 'VOE' mufflers were "Hand-made" for the remaining cars; this occurred in 2006 and 2007, and they are now available from Waldron Antique Exhaust.

The Judge remained available as an option on GTOs. The Judge came standard with the Ram Air III, while the Ram Air IV was optional. Though the 455 CID was available as an option on the standard GTO throughout the entire model year, the 455 was not offered on The Judge until late in the year. "Orbit Orange" became the new standard color for the '70 Judge, but any GTO color was available on The Judge. Striping was relocated to the upper wheelwell brows.

An Orbit Orange 1970 GTO Judge with the 455 engine and Turbo Hydra-Matic transmission was one of the featured cars in the movie Two-Lane Blacktop, which depicted a cross-country race between the new GTO and a 1955 Chevrolet Bel Air.

The new styling did little to help declining sales, which were now being hit by sagging buyer interest in all musclecars and by the punitive surcharges levied by automobile insurance companies, which sometimes resulted in insurance payments higher than car payments for some drivers. Sales were down to 40,149, of which 3,797 were The Judge. Of those 3,797 Judges built, only 168 were ordered in the Convertible form: RA III, RA IV and 455HO. The general consensus is that six of the 168 built were ordered with the 1970-only D-Port 455HO 360 hp engine, a no-cost option, which explains the conflicting production figures over the years as to how many were built; 162 vs. 168. The '69/'70 'Round-Port' RA IV engine, a derivative of the '68 1/2 'Round-Port' RA II engine, was the most exotic high-performance engine ever offered by PMD and factory-installed in a GTO or Firebird. The 1969 version had a slight advantage as the compression ratio was at 10:75:1 as opposed to 10.5:1 in 1970. It is widely-known that PMD was losing $1,000 on every RA IV GTO and Firebird built, and the RA IV engine was highly under-rated at 370 hp. Overall, only a precious 37 RA IV GTO Convertibles were built in 1970: (24) 4-Speeds and only (13) automatics. The three-speed manual, nor A/C, was not available with the RA IV engine. The standard axle ratio was 3.90, with the 4.33 being a low-cost option. Of the (13) '70 GTO RA IV/Auto Convertibles built, only a precious eight received the Judge option. The GTO remained the third best-selling intermediate musclecar, outsold only by the Chevrolet Chevelle SS 396/454 and Plymouth Road Runner.