The 32-year-old singer earned the title after shifting more than 29.6 million singles in her career so far, with 2006 release "Before He Cheats" having been certified five-times platinum by officials at the Recording Industry Association of America, and her recent single "Little Toy Guns" going gold, reported Rolling Stone magazine.
The latest figures place Underwood ahead of fellow country star Jason Aldean, who has sold 23.5 million units digitally to date, but her achievements trail far behind the digital era's bestselling artist Rihanna, who has racked up more than 100 million single sales.