Sir Charles, 84, argues that backing the Yes Campaign is best for both Scotland and for the Scottish Labour Party.
He said: "I am convinced that a Yes vote next September will be the making of Scotland as well as the means for Scottish Labour to reclaim its place at the forefront of Scottish politics and Scottish life."
The former president of the Convention of Scottish Local Authorities has been a member of the Labour Party since he was aged 16. He said he was confident that if Scotland votes Yes next year Labour will be elected the first government of an independent Scotland in 2016.
He said: "I would appeal to all Labour supporters to grab this unique opportunity and to vote for an independent Scotland so that we can start to build the kind of country we want for our families and future generations based on social justice and fairness. I have always been in favour of home rule for Scotland and we have to give credit to Alex Salmond and the SNP for getting us to this stage in the process.
"A Yes vote is the only way to ensure that Scotland gets the kind of government that the people of Scotland choose and that we get rid of a Westminster system that is out of touch with Scottish opinion, priorities and values and imposes such dreadful policies such as the Bedroom Tax.
"I don't believe that whatever government we had in an independent Scotland policies like that would ever be introduced."
Welcoming Sir Charles's support for independence, Dennis Canavan, chairman of the Yes Scotland Advisory Board, said: "Charlie Gray and I go back a long way - about 40 years. He is one of Scotland's most distinguished public servants, having served in local government for around half a century and holding various key positions.
"Charlie Gray is Labour born and bred and the fact that a man of his background and calibre is nailing his colours to the mast of independence will send out a strong signal, especially to traditional Labour voters throughout Scotland."
l The GMB has become the fifth major union to back a No vote. A Better Together spokesman said: "It is a clear sign that the bodies who represent workers in Scotland believe that we are stronger when we work together."