Spears was first rumoured to be in final negotiations with X Factor bosses in March, but the talks apparently stalled when she requested a one year exit clause and a salary larger than $10m.
A source close to the negotiations has now told Deadline that Spears and Simon Cowell have remedied their contractual differences and are close to a deal.
Spears's X Factor contract will apparently see her earn $15m (£9.4m), surpassing the $12m (£7.6) that Jennifer Lopez makes for American Idol.
Cowell and X Factor producers reportedly devoted their time to focus on signing Spears in recent weeks, leaving a decision on a fourth judge until after the 'Toxic' singer inked her deal.
It was reported in late March that Spears has been granted permission from her conservatorship judge to sign an X Factor contract.
Black Eyed Peas star Fergie recently denied that she will be joining The X Factor, insisting that it's simply "not the right time".
Leann Rimes is also believed to be under consideration for an X Factor role.
The second season of The X Factor USA airs on Fox in September. Auditions are under way now, with further details available at thexfactorusa.com
> Simon Cowell on Darren Criss, X Factor rumours: 'I don't know him'
> Stacy Keibler in the running for X Factor USA role?
Watch Britney Spears's 'Circus' music video below: