Cain’s departure set off a competition among other candidates to win over his conservative supporters with voting to start next month in the race to determine the Republicans’ presidential pick for 2012 to oppose President Barack Obama.
Cain, a former Godfather’s Pizza chief executive, told followers in his hometown of Atlanta that “false and unproved” sexual accusations had forced him to suspend his White House bid.
He said he would endorse another candidate, effectively ending a roller-coaster campaign that saw the African-American businessman go from complete outsider to the rising star of Republican conservatives within a few weeks over the autumn.
Cain held a Friday night meeting with his wife, Gloria, who has stayed mostly silent as several women accused her husband of sexual harassment and an Atlanta businesswoman said last week she had carried out a 13-year affair with him.
Gloria Cain appeared at his side on Saturday and smiled throughout his exit speech.
Following Cain’s departure, Newt Gingrich now commands a strong lead in Iowa in the race to become Republican presidential candidate.
According to a new poll, published on Saturday, exactly one month before Iowans become the first in the US to choose their preferred candidate, the Des Moines Register found that Gingrich had the support of 25 per cent of likely Republican voters.
The former speaker of the House of Representatives was seven points ahead of the libertarian Ron Paul.
Mitt Romney – who had 22 per cent of the vote a month ago – has now fallen into third place with a 16 per cent following.