The pop icon, 40, apparently landed the huge deal after sparking a bidding war among publishers desperate for the rights to tell her story now she has escaped a conservatorship.
Her book is expected to detail her rise to stardom as a teenager, her rocky relationship with her family and her life under the conservatorship.
Publisher Simon & Schuster reportedly secured the deal for the pop star’s memoir for as much as US$15m (£11m).
An unnamed source told Page Six: “The deal is one of the biggest of all time, behind the Obamas.”
Michelle and Barack Obamas signed a deal worth an estimated US$65m to write multiple books for Penguin Random House in 2017.
The 14-year conservatorship afforded Ms Spears’ father Jamie Spears complete control over her finances and her career before concerned fans launched the #FreeBritney campaign amid fears she was being held in the arrangement against her will.
Britney’s deal comes days after she accused her sister Jamie Lynn Spears of using a recent interview to sell her new book “at my expense”.
The popstar claimed her younger sister “never had to work for anything” and she had always been “the bigger person”.
In discussion with ABCs Good Morning America, Jamie Lynn said she had “took steps to help” end her older sister’s conservatorship which was formally terminated in November.
She described herself as “my sister’s biggest supporter”.
Responding on Twitter, her older sister said: “I looked at my phone and I see that my sister did her interview to promote her book.
“She was never around me much 15 years ago at that time...so why are we even talking about that unless she wants to sell a book at my expense.
“I wrote a lot of my songs and my sister was the baby. She never had to work for anything. Everything was always given to her.”
