The design began life in a production requirement by American Airlines for a pressurized airliner to replace the classic Douglas DC-3. Convair's original design had two engines and 40 passenger seats. The first Convair 240 flew on 16 March 1947, and production aircraft were first delivered to American on 28 February 1948. Seventy-five were delivered to American, with another fifty going to Western Airlines, Continental Airlines, Pan American Airways, KLM, and Trans Australia Airlines.

The Convair 580 was the conversion from Convair CV-340 or CV-440 aircraft with two Allison 501 D13D/H turboprop engines in place of the piston engines, an enlarged vertical fin and modified horizontal stabilizers. The conversions were performed by Pacific Airmotive on behalf of the Allison Engine Company.