The pop singer tweeted a photo Monday in her wedding gown next to Blackstock. She writes, "I'm officially Mrs. Blackstock."
Clarkson says she tied the knot Sunday at Blackberry Farms in Walland, Tenn., outside Knoxville.
A representative for the singer didn't immediately respond to an email seeking comment about the marriage.
Clarkson was the first winner of "American Idol" and has released five albums and sung multiple pop hits. She has won three Grammy Awards.
Blackstock manages country star Blake Shelton.
The couple has been dating for two years and got engaged last year.