The Lockheed L-649 Constellation was the first real civilian version of the Lockheed Constellation line, as the Lockheed L-049 Constellation was a simple redesign from the military Lockheed C-69 Constellation. The L-649 was planned to be the new standard version of the Constellation, but the L-749 Constellation, an co-jointly produced improved deritative, was chosen over the L-649 by most airlines. Most of the few L-649 aircraft built were delivered and operated by Eastern Air Lines.

When Curtiss-Wright came out with an improved version of the Wright R-3350 Duplex-Cyclone, Lockheed became interested in the project and started developing an improved version of the L-049 Constellation airliner to be powered by this new type of engine. This new project was designated L-049-84. Besides being powered by this new engine, the L-049-84 had a re-inforced wing and fuselage structure, which allowed a higher MTOW than the basic L-049. The cabin was also completely redesigned and more luxurious than before, incorporating changes such as retractable overhead sleeping berths, modernised air conditioning and retractable seats. Ten different cabin layouts were possible. Due to the loudness of the R-3350 engines, the insulation had been augmented through the use of multiple materials including non-inflammable cloth and fiberglass. The problem of overheating that plagued the original engines had been eliminated through the newer design of the R-3350 and the oil tanks being moved away from the engine nacelles. The oil tanks' capacity was also increased by 9 gallons. The payload was also augmented by 1,846 pounds. An extra removable cargo hold was designed to increase the payload of the aircraft. This was called a "Speedpak", and was to be used for shorter flights. The result was a completely new design, causing Lockheed to redesignate the aircraft L-649 due to the large changes.