The win was the second for Smith's professional partner, Cheryl Burke.
Actor Mario Lopez finished second.
"My first impression (of Smith was), he's a big guy," Burke said. "How am I going to get him to ballroom dance? I would never have thought Emmitt could dance the way he can dance now."
Smith praised Burke for her patience, "even when I was stubborn."
"You became a dancer in the last few weeks," Inaba said.
"You're delivering like a true professional," Bruno Tonioli told Smith.
Smith and Burke performed an encore of their samba during Wednesday's broadcast.
The two earlier seasons of "Dancing" were won by singer Drew Lachey and soap star Kelly Monaco.