Flight testing showed that the type had spirted performance and viceless handling characteristics, and the Italian air force began taking delivery of the first of 106 in 1962. Macchi also developed an armed version with underwing hardpoints for bombs, rockets or guns, and increased performance with more powerful versions of the Viper (which was now officially a Rolls-Royce product) and offered it for export.
The MB-326 sold well, particularly in Latin America; it was bought by Argentina, Brazil, Ghana, Paraguay, Togo, Tunisia, the United Arab Emirates, Zaire, and Zambia. The most surprising sale, however, was that of four MB-326Ds to the Italian national airline Alitalia - naturally, these were the unarmed form!
South Africa locally assembled 191 as the Impala Mk. 1, starting in 1966. Australia manufactured 97 MB-326Hs under licence from 1967, choosing the type in preference to the Saab 105, Canadair Tutor, and BAC Jet Provost.
The MB-326, like its competitors the Cessna T-37 and the Jet Provost, was designed and ordered in the period when the "all-through" jet trainer was a fashionable concept in many air forces. The idea was to provide a single type that could be used for both elementary and advanced training right through to near combat-ready standard. In practice it was soon discovered that the simplicity and economy of scale of operating just one type for all training purposes was far outweighed by the purchase and operating costs of a large all-jet training fleet. Most operators quickly added a cheaper piston-engined type for basic training, and the MB-326 found its primary role as a lead-in trainer to prepare pilots for transition to very high performance fighter aircraft.
Although widely liked for its excellent handling and well-suited to its task, the service career of the MB-326 was cut short because of fatigue problems: the Australian fleet, for example, had a life of type extension program in the 1980s and were then re-winged in the early 1990s after a fatigue-related crash, but even so was supplemented by new Pilatus PC-9 trainers to reduce flying hours and the last examples had been withdrawn by 2001.
A single-seat light attack variant of the MB-326, the MB-326K with a further uprated 4000lb thrust Viper engine and strengthened airframe was offered for sale from 1970. It found no buyers to begin with, but from 1974 small numbers were ordered by the UAE, Ghana, Tunisia and Zaire, and 80 were assembled by South Africa as the Impala Mk.2, making it one of the more successful single-seat developments of a two-seat jet trainer.