Under a ten-year deal starting next year the low-cost airline will benefit from lower airport charges if it meets passenger growth targets.
The deal with new owner Manchester Airport Group will create an estimated 7,000 jobs at the site, the Irish carrier claimed.
Ryanair also announced it is launching new routes from Stansted to Bordeaux, Dortmund, Lisbon and Rabat from this winter.
Chief executive Michael O'Leary said it expected to grow passenger numbers by a million a year over the first seven years of the deal.
He admitted that the airline would have to cut fares and reduce margins to meet the targets as well as relocating services from other airports.
Mr O'Leary also said Ryanair was working with the airport to help attract long-haul airlines.
The carrier had threatened earlier this year to cut flights from the Essex airport by 9% because of increased fees, but has now reached a deal with Manchester Airport Group.
The number had fallen from a 2007 peak of 15 million, blamed by Ryanair on increasing fees charged by previous owner BAA.
Announcing the deal with MAG at a London press conference, Mr O'Leary said charges were still "very high".
He added: "We'll be cutting some capacity at other airports for summer 2014 because there's now incentive for us at Stansted to grow aggressively.
"Stansted's already our biggest business but it's about to get an awful lot bigger."
The new agreement is expected to see the airline operate more than 2,000 flights a week from the airport, up from 1,800.
Stansted hopes to increase annual passenger numbers to 30 million a year over the next ten years, making it London's fastest-growing airport.
Offering his thoughts on the airport capacity squeeze facing the capital, Mr O'Leary declared the current official review "pretty much a waste of time" while scoffing at the idea of a "Boris Island " airport in the Thames.
He said the best solution environmentally was for Stansted, Heathrow and Gatwick each to build an extra runway since they all had infrastructure in place, rather than embarking on building a new hub.
"This country has repeatedly proved itself incapable of delivering big infrastructure projects on time and in budget," he said.