He has also featured regularly in the Heineken Cup, racking up 302 points during 42 matches in Europe's premier competition.
Lamb said: "I've really enjoyed my time at Leicester but a lack of game time meant that when the opportunity to join Worcester came up, I didn't want to pass it by.
"I've obviously worked with Dean before at Gloucester and after finding out what he's building at Worcester, I was excited and wanted to be part of that journey and part of that new culture."
Warriors Director of Ruby Dean Ryan said: "I am looking forward to renewing my relationship with Ryan at the Warriors, where we have a different challenge to those we have faced before.
"When the chance to bring him here came up, I didn't want to miss the opportunity to add another talented English back to the team here at Worcester."