1979 would mark the first year of the Fox chassis for Mustang. Originally designed for the 1978 Fairmont, the Fox platform would prove to be a good fit for Mustang, as every ponycar for the next quarter-century would be Fox-based. There would be no convertible until 1983. 1979 Mustang sales surpassed those from 1978 by more than 150,000 units.

For the second time since its introduction, the Mustang was named the official pace car of the Indianapolis 500.

The Cobra model was carried over from the Mustang II. Like all 1979 Mustangs, it featured an egg-crate style grille. The lower body of the Cobra was painted black, a non-functional hood scoop gave the Cobra an aggressive look, and the rear-window louvers were painted the body color. The '79 Cobra was only available as a hatchback.