White -- AKA "Sweet Feet" -- shared the announcement on social media ... in a heartfelt post where he addressed the Pats organization.

"It has been an honor to represent my family, my teammates, and the people of New England as a Patriot!" said White.

"Reflecting on my nine years in the NFL, and all the sacrifices it took to get here, there are many people that were just as much part of this journey."

The three-time Super Bowl champ thanked Robert Kraft and Bill Belichick for "giving me the opportunity to live out my childhood dream" ... calling it a "tremendous blessing" and "honor."

"To say that Foxboro will always hold a special place in my heart is an understatement. It's been the most significant chapter of my adulthood; my kids were born here," James wrote.

"It's the place we know the best as adults and where I have grown and created my family."

Kraft released a statement on White's retirement ... saying, "James White has always been one of the most reliable and dependable players on the field."

"Our fans will remain eternally grateful for his record-setting performance in Super Bowl LI when he helped the Patriots overcome a 20-3 deficit by scoring 20 points, including the game-winning touchdown in overtime."

White -- selected by the Pats in the fourth round of the 2014 NFL draft -- was one of the most reliable weapons for Tom Brady out of the backfield and as a receiver.

The highlight of White's career was his performance in Super Bowl LI against the Falcons. With the game knotted at 28-28 in overtime, "Sweet Feet" scored the decisive touchdown ... sealing the game for the Pats.

JW finished the game with 14 receptions for 110 yards (129 yards total), scoring 3 touchdowns and a 2-point conversion. A legitimate argument could be made he earned SB MVP honors ... and Brady may have agreed. Tom gave James his MVP prize ... a brand new truck.

White only played in 3 games last season ... due to a hip injury that sidelined him for most of the year.

White's ex-teammate, Julian Edelman, showed respect to James' career, writing, "Mr. Reliable. Congrats on a legendary career bubs @SweetFeet_White."

In March, White signed a 2-year, $5 million contract extension keeping him in New England ... but, it appears he's had a change of heart.