"Gary Kenneth Toomey, chief executive of the company has resigned with immediate effect," Jet Airways said in a BSE filing today.
Toomey, who was appointed only last June on a three-year contract, could not be immediately reached for comments.
Ravishankar Gopalakrishnan, the chief financial officer of the airline, will officiate as the "acting chief executive officer" till the board appoints a new chief, the airline said.
It is, however, not yet known as to what led to the sudden exit of Toomey.
Prior to joining Jet Airways, Toomey, an Australian national, had served as president and chief executive of Air New Zealand Group and CEO of Airlines PNG in Papua New Guinea.
Gary Toomey was made the chief executive after the then CEO Nikos Kardassis quit the Naresh Goyal-promoted carrier over some alleged differences with Goyal over the stake sale to the Gulf carrier Etihad.
Kardassis' resignation was announced immediately after Jet agreed to sell 24 per cent stake for Rs 2,058 crore to Etihad last April. The deal was finally concluded last November, though it has been challenged in the apex court.