New security facilities and an enlarged departure lounge will feature in the overhaul, which is being launched today (Thursday, June 20).
Stansted Airport MD, Andrew Harrison, said the investment programme will radically improve Stansted to make it "the airport of choice in London for airlines and passengers alike".
"The way airlines and passengers use the airport has dramatically changed over recent years with far fewer passengers using check-in desks or travelling with hold baggage but spending more time in the departure lounge," he said.
"This exciting transformation project responds to these changing trends and will create a quicker and more efficient security process and bring some sparkle to what is already a fantastic terminal."
The Manchester Airport Group (MAG), which recently took over the gateway, is investing half of the funds with the remainder coming from commercial partners.
The revamp will reflect how air travel has changed since the terminal opened in 1991, said MAG.
For example, the vast majority of passengers at the airport now check in online and over half travel without checked-in luggage, said the airport operator.
To improve the passenger experience, MAG has turned to psychologists to identify points in the airport where travellers feel confused, stressed and relaxed.
MAG is promising a more intuitive and easier journey through the airport, a bigger and relocated security area, double the amount of seating, better restaurants and more shopping choice alongside improved way-finding and additional flight information screens.
Improvements will include:
• Relocated and enlarged security search area
• 22 standard lanes
• Dedicated lanes for families and passengers with reduced mobility
• Fast track lanes for premium travellers
• Reconfigured landside/airside boundary to create a larger departure lounge
• Improved facilities including new and additional toilets
• Significant increase in flight information screens
• New ‘calm zone’ between security and departure lounge
• Complete redesign of departure lounge retail layout
• More seating and space to relax
• More bars and restaurants and a greater choice of shops