Spearing impressed on loan for Dougie Freedman's side last season and the Scotsman made his return one of his summer transfer priorities.
Freedman was concerned whether he would be able to fit the 24-year-old into his squad for financial reasons but a deal has now been agreed with Liverpool.
Blackburn had also been linked with Spearing but withdrew their interest last month 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.
He was also the supporters' choice for player of the year and recently 96% of fans voting in a local newspaper poll called for his return.