The tune, titled "Save the Day", according to Entertainment Weekly, will drop on Friday, August 21, ahead of the October 2 release of the accompanying record, which includes outtakes, demos and b-sides, alongside Mariah's performance from Japan's Tokyo Dome in 1996.
Announcing the new album alongside a picture of the cover art, Mariah tweeted: "This one is for you, my fans. It's to celebrate us, and to thank you for years of pure love and support. I am so grateful to you. THE RARITIES album is out October 2."
The album comes amid the star's #MC30 celebrations, marking 30 years since the release of her self-titled debut album. Since July, Mariah has been releasing weekly digital EPs, featuring remixes and live performances of some of her biggest hits, as well as remastered videos.
Ahead of "The Rarities" dropping, Mariah, who is slated to appear on "Good Morning America"'s (GMA) Summer Concert Series on Wednesday, will release her memoir, "The Meaning of Mariah Carey", on September 29.