The 31-year-old Thompson began his rugby career in the Gloucester academy and had spells with Richmond and Jersey before returning to Premiership rugby with Wasps in 2013.
Thompson said: “Leicester is a club with so much success and prestige – and a history of great opensides like Neil Back and Lewis Moody that I grew up watching play for England – and when the opportunity came along, it was one I couldn’t turn down.
“Playing at Welford Road has been one of my favourite away venues. It’s loud, it’s fierce and the crowd are right there for every hit. I’m looking forward to running out there as a home player.”
He added: “Leaving Wasps is the hardest decision I’ve had to make.
“It’s been my home for five seasons and I can’t thank Dai and the coaching staff enough for the opportunities they have given me.
“Wasps is a special club and I have loved my time here. The fans are incredible and follow us all round Europe; they make the club what it is.
“We have a huge part of the season ahead and I will be working harder than ever to go out on a high.”
Tigers head coach Matt O’Connor said: “Guy is a combative lad in the forward pack, he has a versatile skillset across the back-row positions and we think he adds some more options for us there.
“We look forward to welcoming him in the summer and working with him in the Tigers environment.”
Thompson has made almost 90 appearances in five seasons with Wasps and was nominated for the Premiership Try of the Season for a score against Tigers at Welford Road in 2013-14.
Wasps director of rugby Dai Young said: “We’re sorry to see Guy leave.
“I have no doubt he will remain a fully-committed member of the squad until the end of the season and continue to play his part to the full.
“When the moment is right in May we’ll say our goodbyes more fully. In the meantime, on behalf of everyone at Wasps I’d like to thank Guy for his efforts and wish him well.”
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