Carlisle made his debut for Blackpool in 1997 and went on to make over 500 appearances, also representing QPR, Leeds, Watford, Luton, Burnley, Preston and York. The 33-year-old's final game was last Saturday as the Cobblers were beaten 3-0 by Bradford in the npower League Two play-off final at Wembley.
Carlisle's decision came as a shock to his club manager Aidy Boothroyd, who told the club's official website, ntfc.co.uk: "Clarke's decision was a bit of a surprise."
He added: "He has done well for us, he was part of team who got us out of trouble last season and who took us on this season. He has been strong for us and he formed a formidable partnership with Kelvin Langmead.
"He is a leader and an organiser and for him it is about moving on to the next chapter of his life. We wish him well, I am grateful I have been able to be his manager and for the contribution he has made, not just to Northampton Town, but to football in general."
The Players' union chairman cited concerns about his ability to perform physically as his primary reason to hang up his boots.
He told local reporters: ''It wasn't an easy decision and the fact of the matter is that my body can't do what I want it to any more.
''That's something you learn to deal with as you get older because you change the way you play and you read the game a bit more. 'But this season my body hasn't been able to do what I've needed it to do and that is a completely different thing.''
Carlisle concluded: ''I have thoroughly enjoyed my entire career and especially this season. To be able to contribute to such a good thing that happened this year has been very special to me.''
Carlisle had a year remaining on his Northampton contract, which has been terminated with immediate effect.
Source: PA
Source: PA