The singer will join Simon Cowell and L.A. Reid and will reportedly earn $15 million for a season of the show.
Britney is said to have accepted the deal a few weeks ago, but has worked on the details of the contract.
“The contract is signed,” a source close to Spears revealed. “There’s been a lot of back and forth over the past few weeks, but she’s on. It’s all completed.”
“She’s ready for this,” the source said.
“She can’t wait to sit down next to Simon at the judges’ table and give this everything she’s got,” the insider added.
Also, in March, Louis Walsh claimed that Simon Cowell had contacted Spears in the attempt to make the singer join the show.
Walsh said: “I was out with Simon Cowell during the week, he’s in London. You know like you do and I know he is talking to Britney. He’s definitely talking to Britney to do his American show. Absolutely true!”