As World War II drew to a close, large quantities of military surplus became available on the civilian market along with the cancellation of the remaining C-69 Constellations still in production.
With the Constellation's design at risk, Lockheed purchased the five remaining C-69 transports still in production back from the military, saving 15,000 jobs.
The five aircraft were re-converted into L-049 civilian airliners and put up for sale on the market.
These modifications included removal of the retractable tail stand; along with the inclusion of a luxury interior, more portholes, a galley, and crew relief areas.
Better ventilation, insulation and heating were also added.
The powerplants were replaced by R-3350-745C18BA-1 engines (the civilian equivalent to the wartime R-3350-35).
Design tests did not need to be conducted, as Lockheed had already tasked them to the C-69 aircraft during the war (one of the C-69s also completed the trials for the civilian airworthiness certificate on December 11, 1945).
This made the development of L-049 months ahead of the competing Boeing 377 Stratocruiser, Douglas DC-6 and Republic RC-2 Rainbow (which was still on the drawing board).
89 aircraft had been ordered by November 1945.
 The L-049 was used by TWA, Delta Airlines, Capital Airlines, Braniff, Pan American World Airways, American Overseas Airlines (AOA), Pan American-Grace Airways (Panagra), Air France, KLM, BOAC, El Al, Cubana de Aviación, and other less-known airlines.

The first production L-049 flew on July 12, 1945 and was delivered to TWA on November 14, 1945.
Pan Am received its first L-049 on January 5, 1946.
Due to clauses imposed on Lockheed by Howard Hughes, American Airlines and United Airlines went instead to Douglas and ordered the competing DC-6 (AOA, the overseas subsidiary of American Airlines, still purchased the L-049).
The first commercial flight of the L-049 occurred on February 5, 1946 with TWA's "Star of Paris" flying from New York City to Paris.
The flight lasted nearly 17 hours, stopping over in both Ireland and Newfoundland.
On January 14, 1946, Pan Am began flying its L-049 equipment between Bermuda and New York, replacing the slower Boeing 314 Clipper that flew before it.
AOA, BOAC, and Air France all started L-049 operations later that year.
Due to requests by the airlines, production ceased in 1946, in favor of a more standard civilian Constellation, which became the L-649 and L-749 respectively.

On the evening of June 18, 1947, the Lockheed L-049 Constellation serving Pan Am Flight 121, known as the Clipper Eclipse and crewed by third officer Gene Roddenberry (who went on to create the original Star Trek television series), suffered an engine failure which led to the overheating of the remaining engines until one caught fire, which spread to the aircraft.
When an engine fell from the aircraft, it was unable to maintain altitude, resulting in a crash in the Syrian desert 4 miles (6.4 km) from the town of Mayadin in the early morning of June 19, 1947 and the death of fifteen people.
As World War II drew to a close, large quantities of military surplus became available on the civilian market along with the cancellation of the remaining C-69 Constellations still in production. With the Constellation's design at risk, Lockheed purchased the five remaining C-69 transports still in production back from the military, saving 15,000 jobs. The five aircraft were re-converted into L-049 civilian airliners and put up for sale on the market. These modifications included removal of the retractable tail stand; along with the inclusion of a luxury interior, more portholes, a galley, and crew relief areas. Better ventilation, insulation and heating were also added. The powerplants were replaced by R-3350-745C18BA-1 engines (the civilian equivalent to the wartime R-3350-35). Design tests did not need to be conducted, as Lockheed had already tasked them to the C-69 aircraft during the war (one of the C-69s also completed the trials for the civilian airworthiness certificate on December 11, 1945). This made the development of L-049 months ahead of the competing Boeing 377 Stratocruiser, Douglas DC-6 and Republic RC-2 Rainbow (which was still on the drawing board). 89 aircraft had been ordered by November 1945.  The L-049 was used by TWA, Delta Airlines, Capital Airlines, Braniff, Pan American World Airways, American Overseas Airlines (AOA), Pan American-Grace Airways (Panagra), Air France, KLM, BOAC, El Al, Cubana de Aviación, and other less-known airlines.
The first production L-049 flew on July 12, 1945 and was delivered to TWA on November 14, 1945. Pan Am received its first L-049 on January 5, 1946. Due to clauses imposed on Lockheed by Howard Hughes, American Airlines and United Airlines went instead to Douglas and ordered the competing DC-6 (AOA, the overseas subsidiary of American Airlines, still purchased the L-049). The first commercial flight of the L-049 occurred on February 5, 1946 with TWA's "Star of Paris" flying from New York City to Paris. The flight lasted nearly 17 hours, stopping over in both Ireland and Newfoundland. On January 14, 1946, Pan Am began flying its L-049 equipment between Bermuda and New York, replacing the slower Boeing 314 Clipper that flew before it. AOA, BOAC, and Air France all started L-049 operations later that year. Due to requests by the airlines, production ceased in 1946, in favor of a more standard civilian Constellation, which became the L-649 and L-749 respectively.
On the evening of June 18, 1947, the Lockheed L-049 Constellation serving Pan Am Flight 121, known as the Clipper Eclipse and crewed by third officer Gene Roddenberry (who went on to create the original Star Trek television series), suffered an engine failure which led to the overheating of the remaining engines until one caught fire, which spread to the aircraft. When an engine fell from the aircraft, it was unable to maintain altitude, resulting in a crash in the Syrian desert 4 miles (6.4 km) from the town of Mayadin in the early morning of June 19, 1947 and the death of fifteen people.
Lockheed L-049 Constellation