"It is a girl. [We're] having another girl," he told host Ellen DeGeneres.
Levine and Prinsloo already share 13-month-old daughter Dusty Rose. The singer gushed about Prinsloo, a 28-year-old model, whom he married in Mexico in July 2014.
"She's awesome. She's just, like, a champion of the world. She's killing it," he lauded. "You wouldn't know she's almost seven months pregnant."
The Voice coach also said he and Prinsloo will "probably" have more children in the future.
"I want a lot. I thrive in chaos. I really genuinely enjoy it. We love it," he shared. "She was an only child. She wants, like, 100 babies, but I don't know if I could do that."
Prinsloo announced her second pregnancy in an Instagram post in September. Entertainment Tonight subsequently reported the model and Levine are "over the moon" to welcome another child.
"He and Behati want lots of kids, and they want them close in age," a source said. "Adam is over the moon, as is Behati. They are in love with Dusty and can't wait to make her a big sister."