Britney Spears just signed a massive new music deal … one that sells her rights to her extensive music catalog … TMZ has learned.

According to new legal docs, obtained by TMZ, Britney sold her ownership share of her catalog to Primary Wave, a music publisher.

It’s unclear how much Britney was paid for the music … the exact dollar amount is not in the documents, but our sources described the agreement as a “landmark deal” in the ballpark of the $200-million deal Justin Bieber signed when he sold his music.

The docs show Britney, who’s managed by Cade Hudson, put pen to paper to sell the music on December 30 … and our sources say she’s happy with the sale and has been celebrating by spending time with her kids.

The deal includes Britney hits like “(You Drive Me) Crazy,” “…Baby One More Time,” “Break The Ice,” “Circus,” “Don’t Let Me Be the Last to Know,” “Everytime,” “Gimme More,” “Hold It Against Me,” “I Wanna Go,” “If U Seek Amy,” “I’m a Slave 4 U,” “I’m Not a Girl, Not Yet a Woman,” “Lucky,” “My Prerogative,” “Oops!… I Did It Again,” “Overprotected,” “Piece of Me,” “Sometimes,” “Stronger,” “Till The World Ends,” “Toxic” and “Womanizer” … just to name a few.

The Princess of Pop joins a growing list of artists who have sold their music catalogs in recent years … including huge acts like Bieber, Bruce Springsteen, Bob Dylan, Paul Simon, Neil Young, Shakira, KISS, Sting, Phil Collins, and Stevie Nicks.

Stevie sold an 80% stake in her publishing catalog to Primary Wave back in 2020 … at the time, her copyrights were reportedly valued at about $100 million.