"This really seems like a great family to be part of," Underwood said, as she fought back tears. "I promise I'll do everything I possibly can to not make you regret it."
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 "All-American Girl."
Brooks, who presented her with the induction award - a 14-inch bronze replica of an Opry microphone stand - told her, "Nothing will last as long or be as important as this award right here."
"Being around you five minutes, I can see you get it. In coming from Oklahoma, I know you're sharp as a wit." Brooks, like Underwood, is an Oklahoma native.
The 25-year-old Underwood becomes the latest young addition to the Opry cast 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.