Faulk, 36, retires as the Patriots' all-time leader in career all-purpose yards (12,349) and return yards (5,041). He was selected by the Patriots in the second round of the 1999 NFL draft.
"I've known for about three weeks now," Faulk told ESPNBoston.com. "It was right around the time they were making the announcement of Troy (Brown) being inducted into the (Patriots) Hall of Fame. I held out the last couple of weeks (before making it official). Maybe it was a mourning process."
Faulk, who preferred to save more detailed remarks for his retirement ceremony Tuesday, relayed that he had been in regular discussions with Patriots coach Bill Belichick during the summer. Faulk previously said that if he played this season, it would only be with the Patriots.
"We talked through the course of the offseason and there was still a little chance," Faulk said. "Then one time, he said, 'I think we're going to go with what we have,' and that made (the decision) much more easier."
As for what's next, he tweeted that he is "going to let God's next plan in my life take its course."
Faulk, part of three Super Bowl-winning Patriots teams, was inactive for the Patriots' loss to the New York Giants in Super Bowl XLVI.
"Thanks to all my fans from Louisiana all the way to Mass for believing in me as well as my family for puttin up with. It was a true Blessing," Faulk tweeted.
Patriots wide receiver Matthew Slater praised Faulk, who made his mark as a third-down back, as a central figure of the team's recent success.
"More than anything, he epitomizes the kind of player this organization has built its success on," Slater said on Monday. "The kind of guy who's been unselfish over the course of his career and really stepped up in big moments, but he was a huge role player. He became a star as a role player, made plays for this team time after time in big clutch situations."
Slater said more than anything, he'll remember Faulk's leadership.
"As a leader, he was second to none," Slater said. "He set an example by the work on the field, and by the way he took young guys under his wing in the locker room."
Patriots owner Robert Kraft and Belichick will speak at Faulk's retirement ceremony, which will be held at 10:30 a.m. ET in the Hall at Patriot Place.
The event is open to the public. Those wishing to attend will have to pay an admission fee, but half of all proceeds will be donated to a charity of Faulk's choosing.
Mike Reiss and Mike Rodak cover the Patriots for ESPNBoston.com. ESPNBoston.com contributor Field Yates also provided information.