Her official induction will be May 10.
The former "American Idol" winner sold 7 million copies of her debut album "Some Hearts" and shot to superstardom almost overnight with hits including "Before He Cheats" and "Jesus, Take the Wheel."
Her follow-up album, "Carnival Ride," came out last fall and has produced two No. 1s: "So Small" and her current single "All-American Girl."
Underwood said backstage that the invitation was a complete surprise.
"I felt like I just won something amazing all over again," she said. "The Opry has meant so much to me growing up, seeing people perform and wanting to do that."
Underwood, 25, becomes the latest young hitmaker to become an Opry member in recent years, joining Brad Paisley, Josh Turner and Dierks Bentley.
The Opry, established in 1925, is the longest continuously running radio show in the country. Legends such as Hank Williams Sr. and Patsy Cline were once members of the cast, and contemporary stars including Alan Jackson and Martina McBride are part of today's show, which airs every Friday and Saturday night on WSM-AM.
Opry management says artists are invited to join based on their commitment to the show, as measured by the frequency of their guest appearances, and their overall contribution to country music.