Football: Lallana signs 3-year contract for Brighton
"I think we're at the stage here where we can really push on in the Premier League," Lallana said on Twitter.
"I have got a lot of experience playing in the Premier League and at a high level-I know what's required and how we can improve," he added.
In total, the midfielder has played 443 professional matches, producing 81 goals and making 70 assists.
Lallana won UEFA Champions League trophy, FIFA World Club Championship title, and UEFA Super Cup with his previous club Liverpool.
He also helped the Reds end a 30-year wait for the Premier League trophy.
The 32-year-old will wear number 14 jersey.