Blount had initially agreed with the Niners, but changed his mind after talking to Titans coach Jeff Fisher on Sunday, according to The (Nashville) Tennessean. Since he had not signed a contract, he was free to change his mind.
"I'm not sure quite what happened, but I think it kind of fell in our lap a little bit," Titans general manager Mike Reinfeldt told "The Wake Up Zone" on 104.5 FM in Nashville.
"He's a different kind of halfback than the running backs we have and I think the opportunity is probably better here than it was in San Francisco," Reinfeldt said, noting the Niners have Frank Gore and Glen Coffee on the roster and took Anthony Dixon of Mississippi State in the draft. "They have three kinds of power halfbacks. [Blount's] a different dimension for us."
The Titans also signed undrafted USC running back Stafon Johnson.
Johnson ran for 1,552 yards and 19 touchdowns during his USC career.
The Titans already have Chris Johnson, who ran for 2,006 yards last season as just the sixth NFL player to reach that mark. He was the NFL Offensive Player of the Year.
They also have Javon Ringer, an All-American drafted a year ago.
Blount missed eight games in 2009 for punching Boise State defensive end Byron Hout in the season opener Sept. 3. He also confronted fans yelling at him from the stands and had to be escorted from the field by coaches and security personnel.
Blount returned late in the season and played in the Rose Bowl loss to Ohio State.
He was reinstated late in the season after meeting a number of conditions.
Fisher said in a statement the team talked to a number of people, including Blount, before offering him a deal.
"He was a good college football player who, after talking to a number of people, merits a second chance," Fisher said. "Certainly LeGarrette should understand consequences at this point and we have explained what our expectations are for him to be successful with this opportunity."
Blount went to the NFL combine in February and talked of how he made a mistake by overreacting at the end of the loss to Boise State. He had been projected as a middle-round pick with a resume that included being suspended from the team in February 2009 for not fulfilling team obligations, and also having weight problems.
Blount rushed for 1,002 yards and 17 touchdowns as a junior at Oregon. He had 82 yards on 22 carries in
his suspension-shortened senior year.
The Titans also agreed to terms with centers Kevin Matthews of Texas A&M, son of Hall of Fame lineman Bruce Matthews, and Kenneth Alfred of Washington State; offensive linemen Nick Howell of Southern Cal and John Malecki of Pittsburgh; running back Dominique Lindsay of East Carolina; fullback Willie Rose of Florida Atlantic; tight ends Gerald Harris of Mississippi and Steve Pfahler of Montana; receivers Mico McSwain of North Alabama and Bobby Sewall of Brown; linebackers Jacob Lewko of Pennsylvania and Mississippi's Patrick Trahan; and defensive tackle Joe Joseph of Miami.
The rookies report to Nashville on Thursday and hit the field for orientation Friday.
ESPN.com AFC South blogger Paul Kuharsky and The Associated Press contributed to this report.