Kieran Brookes says it has not been an easy decision to call time on his Saints career.
But the tighthead prop has pledged to give his all for the rest of the season before moving to pastures new in the summer.
Brookes' contract will end at the conclusion of the current campaign and his new club could be confirmed before the end of the week.
He has made 66 appearances for Saints since joining from Newcastle Falcons in 2015.
And the 27-year-old, who has won 16 England caps, said: "This is a decision I have not taken lightly and I’ve thoroughly enjoyed my three years here at Saints.
“I wish all the players and staff at Franklin’s Gardens all the best for the future, and of course I will be giving the team absolutely everything I can on the pitch for the rest of the season to help Northampton move up the Aviva Premiership table.”
Saints still have Jamal Ford-Robinson and Paul Hill under contract for next season.
And interim head coach Alan Dickens said: “We would like to thank Kieran for all his efforts at Franklin’s Gardens over the last three years and we wish him well.
“He still remains fully focused on giving his best for Saints from now until the end of the season, and helping us finish as strongly as possible in the Aviva Premiership and Anglo-Welsh Cup competitions.
“This starts on Saturday when we host London Irish at Franklin’s Gardens.”