"I am suspending my presidential campaign because of the continued distractions and the continued hurt caused on me and my family," Cain told several hundred supporters gathered at what was to have been the opening of his national campaign headquarters.
Cain's announcement follows a string of sexual harassment allegations and five days after an Atlanta-area woman claimed she and Cain had an extramarital affair for more than a decade.
"But because of these false and unproved accusations, it has paid and had a tremendous painful price on my family," Cain said, with his wife, Gloria, standing behind him on the stage.
Whether Cain would stay in the race or drop out was the subject of speculation throughout the week. Even some top supporters who had spoken with Cain were arriving Saturday unsure what he would say.
Cain returned to his Atlanta home Friday and met with his wife. It was the first time they have seen each other face to face since 46-year-old Ginger White came forward on Monday saying she and Herman Cain had carried on a 13-year relationship.
Cain has denied having an affair with White.
Cain had surged in polls until news surfaced in late October that he had been accused of sexual harassment by two women during his time as president of the National Restaurant Association in the 1990s.
The Associated Press contributed to this report.