Spearing, who impressed on loan with Dougie Freedman's side last season, has signed a four-year contract at the Reebok.
Blackburn Rovers had also been linked with Spearing but withdrew their interest after failing to agree terms with the player.
Spearing was Bolton's player of the season in 2012-13, when he played 37 times in the Championship and scored twice.
Freedman said: "Jay wanted to come here and wanted to play for the Bolton Wanderers jersey. He brings qualities to the football club both on and off the field.
"He turned down a few other clubs to come here and he knows and likes the style of our management team.
"We really have to thank the board and owners on this one. The support we've had has been great in helping us to acquire such a fantastic young player."