The representative added that the little girl's name means purpose, which is "one of the seven principles of Kwanzaa" – the annual week-long African American celebration.
Nia is Stevie and Tomeeka's second child. The Higher Ground star also has seven other children from five previous relationships, ranging in age from 39 to one.
The eldest of the Michigan-born musician's children is Aisha Morris, from his relationship with Yolanda Simmons.
Stevie, who has been joined on stage by Aisha numerous times, says his first-born was the inspiration for his hit single Isn't She Lovely.
Grammy-winner Stevie started dating Tomeeka in 2012, following his divorce from Karen 'Kai' Millard Morris, with whom he has sons Kailand and Mandla Kadjay.
Rumours began to circulate that Tomeeka was pregnant with triplets, prompting Stevie to clarify that they were just expecting one child during an appearance on US chat show The View.
"I got, how many, 22 kids?" he joked. "It's not true. The truth is we're going to have a wonderful daughter, born in December, [and her] name is going to be Nia, which means purpose."