Easyjet will move its entire operation at London Gatwick airport into the North Terminal next year.
The news comes four days after it was announced that British Airways will move from the North Terminal to the South Terminal in November 2016 (see news, January 19).
Easyjet currently operates out of both terminals. It will also move into its new home in November next year.
Gatwick airport said it plans to "completely transform" the North Terminal by extending it with increased floor space and investing £36 million on a new check-in area.
The terminal will feature the biggest self-service bag drop in the world, a new departure lounge and a refurbished arrivals area, while £30 million will be spent on a "world-leading security area able to process 5,000 passengers per hour".
The South Terminal will see improvements including a new Pier 1 at a cost of £185 million, featuring new aircraft stands and lounge facilities.
The airport said in a statement: "The BA check-in zone in the South Terminal will also be upgraded and a brand new Premium lounge will be built.
"The South Terminal is also on the same level as the train station – which is to receive a £120 million upgrade - ensuring BA passengers benefit from a quick and easy train to plane transfer."
Lynne Embleton, BA's director of strategy, said: "This is an exciting opportunity for British Airways and our customers. The South Terminal has recently received significant investment to its security area and departure lounge, and we will be working with Gatwick to provide our customers with a new check-in area and lounge.
"The South Terminal also has direct access to trains that run to and from central London."
Easyjet CEO Carolyn McCall added: "Moving to one terminal creates the opportunity for Easyjet and Gatwick to plan and deliver an improved experience for our passengers always delivering on our ambition to make travel easy and affordable for all of our customers.
"Our shared ambition is for Gatwick to be both our biggest and best airport."