Herman Cain suspended his campaign Saturday, saying the accusations of harassment and infidelity have become a distraction.
"I am disappointed that it came to this point that we had to make this decision," the Republican presidential candidate said in Atlanta while his wife, Gloria, stood behind him.
"One of the reasons that I ran for president of the United States was [so] that I could change Washington, D.C., from the inside. Plan B is that we're going to have to change it from the outside."
Cain's campaign came to an end after single mother Ginger White came out earlier this week, saying she and Cain had a 13-year "on and off" physical relationship that ended in March this year.
White described the relationship to MSNBC as a casual sexual affair.
Cain acknowledged that he helped White financially but denied that the relationship went beyond that. At least three other women have accused the businessman of sexual harassment when he headed the National Restaurant Association in the late 1990s.
On Saturday, Cain rejected all the claims as unproven and false.
"America has learned something about this process of running for president," he told supporters. "It's a dirty game. It's a dirty, dirty game. But I happen to believe that the American people are sick of this mess."
He added, "Even though I had to suspend my campaign I have not given up on America."
"We can put united into the United States of America and move this shining city on a hill back to the top of the hilltop where it belongs."
Cain said he plans to endorse a candidate for president in the near future.
GOP presidential candidate Michele Bachmann responded to the announcement, tweeting, "Herman Cain provided an important voice. His ideas & energy generated tremendous enthusiasm for the conservative movement."
"I wish Herman, his wife Gloria, and his family all the best."