The 34-year-old has put pen to paper on a one-year deal and a further 12 months will be triggered if he meets the appearance criteria.
Britton has been rewarded with a new contract after helping the Welsh outfit retain their Premier League status last season.
The midfielder will also be handed a coaching position within the club when he decides to retire from playing professionally.
"Leon has and still is a fantastic servant to this football club," club chairman Huw Jenkins told the club's official website. "He is a model pro and we are very proud to say he is representing Swansea City.
"He has made a tremendous contribution to this club, both on and off the pitch, over the last 15 years. I hope this new contract paves the way for Leon to remain with us for many more years to come."
Britton joined Swansea from Sheffield United in 2011.