Davis, 44, represented Alabama in the U.S. House from 2003 to 2011, and in May, changed his party affiliation to the GOP. In 2008, Davis seconded President Obama's nomination as president at the Democratic convention and in 2010 he lost a Democratic primary when he sought to run for governor of Alabama.
Davis told The Washington Post Thursday he will use his time on the podium in Tampa, Fla., to call for defeat of the president he once backed, citing his disillusionment with Obama. "The one thing I can bring to the table is to be something of a voice for that group of people," he said.
Davis, who now lives in Virginia, spoke at a Romney campaign event in Ballston Wednesday and attacked Vice President Job Biden's recent comment that the likely Republican presidential nominee would put African-American voters "back in chains."
He told CNN Biden's comment was divisive and insulting and "ought to embarrass President Obama."
A Republican convention organizer confirmed Davis will speak during the convention which runs from Aug. 27-30, but the date has not been announced.