"So hard to believe it's been 10 years!" Underwood wrote on her Instagram post, adding, "I'm forever grateful to American Idol for changing my life! #blessed."
The caption accompanied a throwback photograph of Underwood on the "American Idol" stage taken shortly after she was announced as the winner.
Underwood, 32, beat out finalist Bo Bice to win that season of the show, and she's since become one of the most successful performers to emerge from "American Idol", which will enter its final season next year.