Producer Fred Gaudelli said that after Hill informed him in February, Underwood was the only performer he pursued. She was under consideration for the role when NBC first broadcast the Sunday night NFL games in 2006.
Pink sang the opening tune, set to Joan Jett's "I Hate Myself for Loving You," for that first season before Hill came on.
"For me, it just always seemed like something that would be fun to do," Underwood said during a conference call. "To watch Faith do it week after week, to see that hype for the game, it's something that's so cool."
Underwood plans to adapt the intro to her style, with the lyrics remaining the same. NFL stars will again appear in the video sequence.
A former "American Idol" champion and six-time Grammy winner, Underwood is married to hockey star Mike Fisher of the Nashville Predators. The 30-year-old Oklahoma native sang the national anthem at the 2010 Super Bowl.
Underwood said her husband, who's friends with several NFL players, was thrilled about her foray into his profession.
"He's a sports dude," she said. "Yeah, he plays hockey, but he definitely loves football, as do I."
The first Sunday night game is Sept. 8, when the New York Giants visit the Dallas Cowboys. "Sunday Night Football," which averaged 21.8 million viewers last season, is TV's top-rated prime-time show.
Gaudelli said he contacted Hill's reps Tuesday to let them know of the hire. Underwood said she expected to get pointers from Hill the next time they cross paths.
Underwood is signed up to star in NBC's live broadcast of "The Sound of Music" this year. While her familiarity with the network helped, she said, the two deals weren't connected.