The agency has handled the company's creative and media duties since 2000. The business is estimated to be worth £6 million.
Vinod Nair, Network Advertising's managing director, said that it had been "a great journey" working with the airline company over the past six years.
Jet Airways is now expected to call a competitive pitch for both its media and creative duties. It is unknown whether it will look for one agency to work on both.