Cain, who has never held public office, had previously formed an exploratory committee, the first step toward a full-fledged bid.
Cain has a long way to go to boost his name recognition now that he's officially in the race. According to Gallup, only 29% of Republicans even know who he is. But as Cain spokeswoman Ellen Carmichael told TPM this week, the campaign is pleased with the amount of positive feedback they've received so far, and believes Cain's stock will rise as more people get to know him.
By making his campaign official, Cain joins Rep. Ron Paul (R-TX) and Newt Gingrich as the only declared candidates in the race. Tim Pawlenty is expected to declare his candidacy on Monday, and several others candidates who have formed exploratory committees and are expected to join the race in the coming months.