The 33-year-old striker, who recently returned to the b2net Stadium after a loan spell at Torquay, has had his contract terminated by mutual consent.
"Martin is a true professional and everyone at Chesterfield wishes him all the best for the future," said Spireites boss John Sheridan.
Gritton added: "I love football but understand it doesn't always work out, so we move on. I am pleased that Chesterfield is having some success and I wish everyone well for the future."
Gritton joined Chesterfield from Macclesfield in January 2009 and scored five goals in 30 appearances for the north east Derbyshire club.