Fairchild Republic and Northrop each built two prototypes for evaluation under the US Air Force's A-X programme, initiated in 1967, for a close support aircraft. The first Fairchild Republic prototype, designated YA-10A, flew for the first time 10 May 1972. It was announced 18 January 1973 that Fairchild was the winner of the competitive evaluation of the prototypes, and received a contract for six A-10A aircraft, the first of which flew 15 February 1975.

The first flight by a production A-10A Thunderbolt II was made 21 October 1975. Purchase of a total of 739 aircraft was planned; but funding was terminated in 1983 after a total of 713 production A-10s had been ordered and delivered. Delivery was completed 20 March 1984. Northrop Grumman acquired the A-10 programme from Fairchild in 1987. The Thunderbolt II was used during the 1991 Gulf War.

Export versions of the A-10 were available as single-seat night attack and two-seat combat-ready trainer aircraft. Night capability is provided by the addition of a Westinghouse WX-50 radar, Texas Instruments AAR-42 FLIR, Litton LN-39 inertial navigation system, Honeywell APN-194 radar altimeter, AiResearch digital air data computer, Ferranti 105 laser range-finder and Kaiser head-up display. It is expected that night/adverse weather capability can be improved with the addition of a LANTIRN (Low-Altitude Navigation Targeting Infra-Red for Night) fire-control pod.

The first combat-ready A-10A wing was the 345th Tactical Fighter Wing, based at Myrtle Beach, South Carolina, to which deliveries began in March 1977.