The new 3,650sq ft Runway Bar, which cost £1.3m to develop, is on a new mezzanine level at the rear of the existing pub and can seat up to 200 customers.
Guests will be able to watch planes landing and taking off through a 30-metre long window in the new bar area.
The Runway Bar is in addition to the 7,000sq ft of customer space on the existing ground floor and mezzanine level of the Windmill, which already serves more than 1.2m punters a year.
The new bar will serve six real ales, at all times, including an ever-changing range of beers from local and regional brewers and microbreweries, alongside craft beer and lager from around the world.
New self-service coffee machines have also been installed throughout the pub, offering free refills on a range of coffee and tea choices.
The Windmill opened at its current site in March 2015 at a cost of £2.7m, replacing the JDW pub of the same name, which has been at the airport since May 2003.
The pub, which will continue to be managed by Michael Wilkins who has worked there since 2007, will employ an additional 40 staff, to the existing 175 members already on the team.
Manager Michael Wilkins said: “The Runway Bar is fantastic addition to the Windmill pub and we look forward to welcoming and serving even more JDW customers, travelling through Stansted Airport.”
Stansted Airport head of retail F&B and duty free Richard Cross hailed the new bar and how it will improve guest experience.
He said: “The Windmill’s new bar is a fantastic new addition at London Stansted and represents the culmination of phase one of the international departure lounge enhancement works within our transformation programme.
“The new runway bar brings a further 200 seats with excellent views over the runway giving customers and holiday makers breath-taking views of all the aircraft as they land, take off and taxi.
“JDW is a market leader in pub management with a track record of excellent success at London Stansted. We are very proud to have worked closely on this exciting project and look forward to welcoming even more guests every year to enjoy the great service, food and drinks the Windmill has become famous for.”