The Scottish singer, who rose to fame after winning the second series of the talent show Pop Idol, said she believed a Yes vote was "an opportunity for change".
She said: "Let's be honest, there is of course an element of risk by voting for independence because there are simply no guarantees, but isn't that the case with most things in life?
"And there are certainly no guarantees if we vote No. The main difference is the people of Scotland will be in the driving seat."
The singer compared her decision to vote Yes to the chance she took in entering the competition more than 10 years ago.
She said: "We take a leap of faith every single day, whether it's buying a house, choosing university courses, deciding to start a family with no idea what the future will hold so why do we do this? Because we believe in ourselves and I believe that we the people of Scotland should absolutely have and hold the power to our own destiny.
"Scotland is full of talented people and I think a Yes vote on September 18 is the once in a lifetime chance to give more opportunities for these people."
Yes Scotland chief executive Blair Jenkins said: "Like Michelle, more and more people all over Scotland are waking up to the tremendous opportunity that a Yes vote offers them and future generations."