The couple announced the pregnancy news last month, and the 25-year-old singer and Danielle have now revealed the gender of their first child together, reported Us magazine.
"We're having a girl ... I am going to be a father to a little girl! Mind blowing. So excited," Kevin said in an online post.
The revelation was originally set for the Jonas iTunes application before the server crashed and fans were directed to a different site.
Tweeting after the announcement, the father-to-be wrote, "It is a girl! Thank you everyone! She's sucking her thumb! (sic)."