Perry, 32, is the first major name to come aboard the reboot of the show, which was canceled by Fox Broadcasting last year after 15 seasons amid declining viewership ratings. The new "American Idol" will air in 2018.
"I'm always listening to new music, and love discovering diamonds in the rough - from mentoring young artists on my label, or highlighting new artists on my tours, I want to bring it back to the music," Perry said in a statement from ABC, which is owned by Walt Disney Co.
No other judges have been named yet.
Grammy-nominated Perry has been a pop powerhouse since her breakthrough single "I Kissed a Girl" in 2008, and is known for upbeat songs such as "California Gurls" and "Firework," gimmicky outfits and vibrant, colorful performances geared toward a young audience.
"American Idol," a competition open to the public, launched the careers of singers such as Kelly Clarkson, Jennifer Hudson and Adam Lambert, aided by celebrity judges who alternately feuded and fawned over discovering new talent.
At its peak from 2005 to 2007, the show was watched by more than 30 million viewers, but by 2014 only 10.6 million viewers tuned into the "Idol" season finale.
Overall television consumption has declined in recent years, hurting live shows as more home viewers watch on-demand content.
NBC's rival singing competition "The Voice," which features a panel of four celebrity judges, has grown in popularity. Its season 11 finale in December drew 12.1 million viewers.