The midfielder impressed during a season-long loan spell at the Reebok Stadium last season, scoring two goals in thirty-seven appearances before being named the clubs player of the season.
Fellow Championship side Blackburn Rovers had also been linked with a move for the 24 year old, but withdrew their interest after failing to agree personal terms with the player.
Spearing broke into the Liverpool first team in 2008, making his debut in the 3-1 Champions League group stage victory over PSV Eindhoven at the Philips Stadion.
He made fifty-five appearances in all competitions for the Merseyside club, having also spent the last part of the 2009/10 campaign on loan with Leicester City.
He becomes the ninth new arrival at Bolton this summer, and has been included in the squad to face Reading at home on Saturday afternoon.