The Patriots also re-signed linebacker Tully Banta-Cain, a team source told ESPN NFL Insider Adam Schefter.
Galloway, a 15-year NFL veteran, has seven receptions for 67 yards this season. He has not been on the Patriots' active roster for the past three weeks.
Galloway struggled with the offensive system and was inactive the last three games after catching just seven passes in the first three.
"He's had a great career and this is one of those things that just didn't work out," Patriots coach Bill Belichick said. "I don't think it's anybody's fault or anything that you just pinpoint."
The Patriots play Sunday against the Tampa Bay Buccaneers where Galloway, 37, spent the past five seasons. He was the eighth player drafted in 1995 and spent five years with Seattle before playing four with Dallas.
He caught 689 passes, which was eighth among active receivers, for 10,777 yards and 77 touchdowns.
Banta-Cain was unexpectedly cut loose Monday, but the Patriots agreed to a contract extension through 2011, a source familiar with the deal told ESPNBoston.com's Mike Reiss.
Banta-Cain's extension boosts his 2009 base salary from $620,000 to $1.8 million, according to the source. He'll earn base salaries of $1.3 million in 2010 and $1.5 million in 2011, and will have a chance to earn additional money in the form of playtime and Pro Bowl incentives in the final two years of the pact.
Banta-Cain is tied for the team lead with three sacks. He's played in all six games (13 tackles), with two starts, and has been a solid contributor on special teams as well.
The Patriots are in the process of striking a similar deal with linebacker Eric Alexander as well, multiple sources familiar with that negotiation said. Alexander's main contributions come on special teams.
In other moves, the Patriots released tight end Michael Matthews. He played in three games this season as a reserve tight end and on special teams.
"He came in late and started learning the stuff from the start of the regular season after missing all training camp" with the Patriots, Belichick said.
Those roster spots probably won't be filled before Friday, he said.
Two possibilities for those are tackle Mark LeVoir, who was on the physically unable to perform list, and wide receiver Brandon Tate, who was on the non-football injury list. Both participated in Tuesday's practice, a walkthrough, and must be activated within 21 days or go on a list that would keep them from playing the rest of the season.
They're almost certain to be back during those 21 days, but Belichick indicated it wouldn't happen this week.
"I don't know if a player, after a couple of days of practice, is going to be ready to play," he said. "It's a possibility, but I think it's a lot to ask."
Thomas, a healthy scratch in Sunday's 59-0 win over the Tennessee Titans for the first time since his rookie year in 2000, practiced Tuesday.
Asked if he was leaning toward activating him Sunday, Belichick said, "as we always do, we'll activate the players that we feel give us the best chance to win this game."
Morris didn't return after hurting his left knee on the Patriots' third offensive play against the Titans. Is Belichick confident he'll play again this season?
"Sure," he said. "If the player wasn't going to be back during the season, then we'd place him on injured reserve."
With Fred Taylor having missed the last two games following ankle surgery, the Patriots could be down to three running backs -- Laurence Maroney, Kevin Faulk and BenJarvus Green-Ellis -- against the Buccaneers.
"We've gone into games with three running backs before," Belichick said.
It's the game that counts more for Belichick than the Wembley Stadium venue as the NFL widens its visibility with its third game in London.
"I'm sure it'll be something we'll all remember," Belichick said, but "I'm just trying to coach a team. I'm not trying to solve the world's problems."
Mike Reiss covers the NFL for ESPNBoston.com. Information from The Associated Press was used in this report.