Blackstock proposed to Clarkson last December. The couple have been dating since 2011.
"He's not only singing, he's marrying us," Clarkson told "Entertainment Tonight" of Shelton at the Academy of Country Music Awards in Las Vegas Sunday. "He totally is; he's done it before with people."
Clarkson did not disclose the date or location of her wedding, but said she does have a dress for the occasion.