Downing spent the last two seasons of his career with Blackburn Rovers in the Championship, where he made 19 appearances last season.
Downing started his career with Middlesbrough, where he returned for a second spell in 2015 and made 404 appearances in total for the Teeside club.
He also turned out for Aston Villa, Liverpool, West Ham United and won 35 caps for the Three Lions of England.
He said in a statement: "After some time to relax and reflect with my family over the summer, I have decided the time has come to retire from playing professional football.
"First and foremost, I would like to give a big thanks to my mum and dad, my sisters, and of course my wife and 2 kids for all their support and help throughout my career.
"I would like to give a special mention to my dad, who has been the single biggest influence on my career and I am grateful for everything he has done for me.
"I would like to thank all the football clubs I played for during my career and all of their fantastic fans and staff. I’d also like to thank all of the great managers I played for. As I kid I could have only dreamed of playing for the teams I played for and of getting to share the pitch with some of the players I shared a pitch with. I played with and against some unbelievable players over the years.
"I look back on the 35 times that I played for England with immense pride and I made some incredible memories that will last a life time. I feel very lucky and fortunate to have had the career I had.
"I am excited for the future whether that be in the media, coaching or management. I have learned a lot from the game over the years and gained a lot of experience that hopefully I can pass on to others.
"Thanks for everything."
