Eight flights had to be diverted – two from Thomas Cook, one Thompson service and five operated by EasyJet.
The BA Airbus A320, coming in from Naples, touched down at about 12.30am on Friday.
A spokesman for the airport told Sky News the plane spilled 90 litres of hydraulic fluid after it landed.
The “priority landing” was requested as a precaution after a technical fault, British Airways said.
Once the jet was safely on the ground it was inspected and the main runway closed.
No one was injured and passengers were able to disembark a short time later, while other planes were diverted to the airport’s standby runway.
The main runway was reopened at about 5am after it had been washed down and friction tests conducted to ensure it was not slippery.
“Our flight landed safely after our pilots requested a priority landing as a precaution after a technical fault,” British Airways said in a statement.
“The safety of our customers and crew is always our top priority, and our engineers are currently conducting a thorough check of the aircraft.”
Gatwick said today’s flight schedule had not been affected.