The former Southampton winger's double, along with Alberto Moreno's opener and Jonjo Shelvey's own goal, enabled Brendan Rodgers' side to end the year on a high
Alberto Moreno handed Brendan Rodgers’ side a half-time lead with a goal before the break, while Lukasz Fabianski gifted the hosts with a second when his attempted clearance hit Lallana and looped into the net.
Gylfi Sigurdsson pulled a goal back one minute later but Lallana’s superb individual effort restored Liverpool’s two-goal advantage before Jonjo Shelvey headed Jordan Henderson’s cross into his own net.
Liverpool head into 2015 with just one defeat in their last 10 games in all competitions and move above Swansea into eighth place.
Simon Mignolet was recalled to the starting line-up to replace the injured Brad Jones and captain Steven Gerrard dropped to the bench as Rodgers made four changes to the side that won at Burnley on Boxing Day.
Wayne Routledge replaced the injured Jefferson Montero in one of three changes to the Swansea team following the home victory over Aston Villa.
Swansea were allowing Moreno too much space on the left in the opening stages and the Spaniard whipped in a cross that Raheem Sterling met with a first-time strike that brought a fine reflex save out of Fabianski, with Lallana firing over the crossbar on the follow-up.
Liverpool appeared to have lost their way in the first half after a promising start, but Moreno put them in front after 33 minutes.
The former Sevilla man was left unmarked inside Swansea's box and had the simple task of turning in Henderson's ball in from the right to round off a slick passing move.
Shelvey was fortunate not to get sent off before half-time after his swinging arm caught Emre Can in the face.
After the restart, the game’s tempo increased and Liverpool doubled their lead after Fabianski’s indecisiveness on the ball allowed Lallana to close down and deflected the attempted clearance into Swansea’s net.
Liverpool were guilty of switching off after scoring once again as Mamadou Sakho beat Wilfried Bony in the air, but could only head the ball into the path of Sigurdsson and he fired home from close range just a minute after Lallana’s goal.
Sterling came close to restoring Liverpool's two-goal advantage soon after when his strike came back off the post after Henderson picked him out with a superb cross from the right flank.
Lallana was fortunate with his first goal, but there was nothing lucky about his second as Philippe Coutinho laid the ball off to the midfielder with a deft flick and he dribbled through Swansea’s defence before finishing with his left foot.
Liverpool were out of sight in the 69th minute when Shelvey got his head on Henderson's corner but could only watch as the ball looped just inside the far post.
Sterling was lucky to get away with swinging an arm at Federico Fernandez after the ball had gone out of play, while substitute Bafetimbi Gomis' strike rattled the crossbar but Liverpool were able to coast to victory and end the year on a high note.