Capped 62 times by England, including successive World Cup Finals in 2003 and 2007, Kay joined Tigers from Waterloo and made his club debut in September 1999.
He has now made a total of 281 first-team appearances and is one of the most decorated men in English rugby history, winning five Premiership titles, an Anglo-Welsh Cup and playing in four Heineken Cup Finals, including the historic back-to-back wins in 2001 and 2002.
Kay, 34, said: "I've had 11 fantastic years at Leicester Tigers and this has been a very important part of my life.
"I've played alongside some legends of the game with Leicester and I have some great memories of my time with the club.
"Welford Road, in particular, has been very good to me and I've enjoyed so many great occasions at the stadium over the years.
"I'd especially like to say thanks to all of the fans for their great support over the years.
"Although I am obviously disappointed there wasn't room for me in the squad here next year, I would like to wish everyone involved with the club my very best wishes for the future. Now I have reached a point in my life where I have to consider what happens next. I will concentrate fully on making whatever contribution I can to Leicester Tigers in what remains of this season and I have a number of options to consider for the future. I will make a decision on my immediate future during the summer."
Awarded an MBE in recognition of the Rugby World Cup win in 2003, Kay played in two Tests with the British & Irish Lions on the tour to New Zealand in 2005, on top of his many honours at club level.
Tigers head coach Richard Cockerill said: "Ben has been a brilliant servant of the club for over a decade and a genuine world-class operator with the club, with England and the Lions.
"He has shown true commitment to the Leicester Tigers shirt since he arrived in 1999, his individual skills, his leadership and his work for the team have taken him right to the top of the game and kept him there for a long period of time.
"I know Ben has several options open to him for the future, and we wish him well in whatever he does. Ben and his family will always be welcome at Welford Road."
As part of Ben's testimonial, supporters have the perfect opportunity to meet the players - and say their farewells to him, Aaron Mauger, Lewis Moody, Sam Vesty, Mefin Davies and Brett Deacon who are moving on this summer - at a Beers With The Boys evening at Welford Road on Tuesday, May 25. Tickets are available now, price £25 including complimentary beer on arrival, bangers-and-mash supper, an interactive Q&A with the players and a £10 ticket to enter an exclusive Spot The Ball competition which could win you a £40,000 BMW. Donations from sales will be made to Ben's nominated charities Help for Heroes, the Matt Hampson Trust and The British Heart Foundation. Tickets are available from Cathy Bown at Ben Kay Testimonial, call 01455 441964 or 07876 500 632, or email [email protected]