Leicester Tigers confirm five summer signings
Lamb played against Tigers for Northampton in Saturday's Premiership final.
"It is important that we have good strength and depth. We feel they can all make a big contribution here," said director of rugby Richard Cockerill.
"Four of those players have extensive Premiership experience."
He added: "Owen Williams is a young man with a lot of ability and potential which we believe can be developed within the Tigers squad."
Leicester have already confirmed the arrival of prop Jerome Schuster and scrum-half David Mele from Perpignan this summer, with Mot-de-Marsan second row Sebastian De Chaves also agreeing a deal with the East Midlands outfit.
Lamb, 27, who made 55 appearances in all competition for Northampton since moving to Franklin's Gardens from London Irish 2011, was a second-half replacement in Saints' 37-17 Premiership final loss to Tigers on Saturday.
It is the second time the England Saxons player has lost Twickenham's showpiece event to Leicester, his first defeat coming in 2007 while playing for Gloucester.
Cockerill said the club would continue to relish their record 10th English title before planning for the 2013-14 season.
"Right now, it is just good to send guys like Matt O'Connor, Martin Castrogiovanni and Geordan Murphy on their way with a victory," Cockerill said.
"We will have a couple of weeks off then come back in and try work out how we do it all again."