The gossip site posted a picture from the New Orleans auditions that showed Klum's name alongside the other judges.
View slideshow: "America's Got Talent" New Orleans Auditions
NBC officially announced the news on Monday in a press release, which notes that this will be the first time the show has had a four-judge panel.
"Heidi has an amazing career across multiple media platforms, and has built a brand that is a force in the entertainment business," NBC's head of alternative and late night programming Paul Telegdy said in a statement.
"...As we look to develop an act that will get the world’s attention, we and the contestants will benefit from Heidi’s international sensibility and understanding of what works in today’s global entertainment industry.”
The former supermodel has hosted the Victoria's Secret Fashion Show numerous times, and has also hosted "Germany's Next Top Model" since 2006.
She received an Emmy nomination in 2008 for her hosting duties on "Project Runway," for which she also serves as executive producer. She will continue on the show through her stint of "AGT."
"I'm really excited to join the panel of 'AGT' to see it all -- from the ridiculous to the fantastic," Klum said in a statement. "I love the surprise element of the show and not knowing what we'll see next and who will wow us. I'm also looking forward to spending time with my fellow judges."
Mel B joined the reality competition series last month, replacing "The Talk" co-host Sharon Osbourne, who left the show over a dispute with NBC over their alleged firing of her son Jack from "Stars and Stripes" after he was diagnosed with multiple sclerosis.
"America's Got Talent" will return for Season 8 in May, while Klum can currently be seen on "Project Runway" Thursdays at 9/8 p.m. CT on Lifetime.