Spears' spokeswoman, Nicole King, confirmed Friday that the documents formalizing the marriage were filed on Thursday, although she wouldn't say in what California county.
The "Oops! ... I Did It Again" singer, 22, married her fiance, 26-year-old Federline, at a private home in the Studio City area with 20 to 30 people attending.
Days later, celebrity gossip magazines questioned whether the event was a hoax because no paperwork for the marriage could be located in any government office.
Federline has said the delay was caused when the couple moved their wedding date up to Sept. 18 as word leaked out that they were planning to be married on Oct. 16. Moving the date up a month, he said, didn't give their lawyers time to finish their prenuptial agreement.
In an interview with People Magazine before the nuptials were official, Spears said, "I know we're not completely legal until we file the license, which we'll do next week. But in a real sense, a spiritual sense, we're married."
Spears and Federline announced their engagement in June after dating since early this year.
Federline appeared in the movie "You Got Served" and performed as a backup dancer for singer Justin Timberlake, Spears' former boyfriend. He was previously involved with actress Shar Jackson of TV's "Moesha." They have two children — a 2-year-old and a newborn.
In January, Spears married childhood friend Jason Alexander in a surprise wedding in Las Vegas. That marriage was annulled 55 hours later.