The 22-year-old's previous deal expired was due to expire in the summer and he has been linked with moves to Newcastle, Fulham and Wolves.
But Lallana, who has scored eight goals this season, has now committed his future to the League One promotion chasers.
"We've got a long-term vision at this football club and we want Adam to play a part in it," manager Nigel Adkins told the club's official website.
Source: PA
Source: PA