Gritton joined the Spireites from Macclesfield in January 2009 and made 30 appearances, scoring five goals.
He told the club website: "I love football but understand it doesn't always work out, so we move on."
He added: "I am pleased Chesterfield is having some success and wish everyone well for the future."
Chesterfield manager John Sheridan said: "Martin is a true professional and everyone at the club wishes him all the best for the future."
Gritton has previously played for Plymouth, Grimsby and Lincoln.
Source: BBC Sport