The England international made 648 apperances for the Blues after moving from West Ham United in 2001, scoring a club record 211 goals, but manager Jose Mourinho has decided not to offer the veteran a new deal.
At 35, Lampard struggled to hold down a regular place in Mourinho's lineup during the 2013-14 campaign, making just 20 starts, and though he has hinted at retiring after the World Cup, rumors persist that he will move to MLS.
"When I arrived at this fantastic club 13 years ago I would never have believed that I would be fortunate enough to play so many games and enjoy sharing in so much success. This club has become part of my life," he said in a statement. "Roman Abramovich, the man who saved our club and took us all to new levels. His desire to push the club to the top of the football world has rubbed off on everyone.
"All the managers and coaches who have helped me develop my game during the time I have been here. I have learnt from every one of them."
"The club will move forward, and as a Chelsea man I have no doubt that with the quality of the players that are there, they will continue with the success that we have all enjoyed over the past seasons," he continued. "Thank you for the memories and keep making history!"
Lampard leaves Chelsea as one of the club's most successful players in their history, having won three Premier League titles, four FA Cups, two League Cups, the Champions League and the Europa League.
He joins international teammate Ashley Cole in leaving the club, with Samuel Eto'o also set to leave as Mourinho looks to build on a trophyless season in West London.