The midfielder spent most of last season on loan with the Trotters, featuring in 37games, and boss Dougie Freedman had made capturing him on a permanent basis one of his highest priorities this summer.
Spearing, who signed a four-year deal, endeared himself to the Bolton faithful last year which led to many fans chanting his name during the draw with Burnley last Saturday.
"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," Freedman told the club's official website.
"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."
The midfielder could go straight into the Trotters' side for the weekend tie against Reading with boss Dougie Freedman sweating over the fitness of Chris Eagles.
- Sports & Recreation
- Dougie Freedman
- Bolton Wanderers