The source told E! News: "The contract is signed. There's been a lot of back and forth over the past few weeks as they negotiated the small details, but she's on. It's all completed and Britney is beyond excited,
"She's ready for this. She can't wait to sit down next to Simon at the judges' table and give this everything she's got. She is excited about showing the world that she can do this, and do this well."
They added: "This is the perfect next stage in her career. Both Britney and Simon are very excited to work together."
While the Hold It Against Me hitmaker may have allegedly landed a judging role on the show, Disney starlet Demi Lovato has been linked to land the final vacant seat on the XF USA panel - with Lovato previously telling MTV News UK that the job would be "a dream come true."
There is still no official confirmation from either Britney or The X Factor USA regarding E! News' allegations, but keep it MTV.co.uk for more news on this story.