The Aussie billionaire proposed to the pop star with a sparkling 35 carat ring.
A rep for the duo confirmed the exciting news to Daily Mail Australia.
"Yes, the couple were engaged tonight in New York," the spokesperson said.
E! News revealed that James "popped the big question in her hometown tonight, and he presented her with what can only be described as the most breathtaking engagement ring."
According to sources close to Pariah no official wedding date has been set.
TMZ reported James organised a private dinner at Eleven Madison Park in New York with a group of Mariah's closest friends so the precious moment could take place "in front of the most special people in her life."
Speaking of their whirlwind romance recently, Mimi gushed: “We first met in Aspen [Colorado]. We were at the Hercules premiere. We were talking and laughing, and people were getting mad at us and stuff like that. So we hit it off."
Their romance has moved at rapid pace with James often lavishing the mother-of-two with extravagant gifts. Most recently, he spoiled her with a $500, 000 diamond choker.
“Oh, this old thing?” she said with a sly grin. “This is a Van Cleef [& Arpels] piece that my new beau got for me recently.”
She described the gift as a “very, very big surprise” that was “really nice” of James.
The Barangaroo billionaire is expected to join Mimi as she begins the third leg of her sell-out Las Vegas residency at Caesars Palace, before she embarks on a world tour.
Mariah was previously married to actor Nick Cannon, with whom she shares four-year-old twins Monroe and Moroccan Carey, and music exec Tommy Mottola, who she divorced in 1998.
While James was married to Erica Packer from 2007 to 2013 and shares three children, Indigo Packer, seven, Jackson Packer, five and Emmanuelle, three.
He was previously married to Jodhi Meares from 1999-2002 and before finding love with Mariah enjoyed a secret romance with supermodel Miranda Kerr.