"Upon completion of our internal review of the Flight 345 accident, last week the captain was terminated and the first officer is being required to undergo additional training," Southwest spokeswoman Whitney Eichinger said in a statement.
The carrier added that it was cooperating in the National Transportation Safety Board probe of the incident.
The NTSB said in August that it found the jet's two pilots exchanged control of the Boeing 737 plane shortly before the landing on July 22.
The airplane was less than 400 feet off the ground when the pilots switched duties, with the captain taking the controls and the first officer monitoring the instruments, the NTSB said.
The plane, heading to New York from Nashville, Tennessee, touched down at LaGuardia on its front landing gear, which is not designed to take such weight, according to industry experts. The nose gear collapsed and the plane's electronics were damaged. Nine people had minor injuries.
Shortly after the incident, Southwest said landing on the nose gear before the main landing gear touched down was not in line with its normal procedures.
The captain had worked at Southwest for more than 10 years, with six years as captain and more than 12,000 flight hours, including more than 7,900 hours in a 737, the NTSB said in August.
The first officer had logged 18 months with the airline and had about 5,200 flight hours, according to the U.S. safety agency.
Southwest did not disclose the identity of the pilots.