Kerik, the former police commissioner of New York City and one-time Bush Cabinet nominee said at a news conference that he had apologized to Giuliani for being a distraction because of his to head the Department of Homeland Security.
Kerik had been CEO of Giuliani-Kerik LLC, an affiliate of Giuliani Partners LLC. In a statement Wednesday, Giuliani said Giuliani-Kerik would be renamed Giuliani Security & Safety.
Kerik said he told Giuliani his resignation would be effective immediately. He said he would seek other unspecified business opportunities, and did not take questions from reporters.
President Bush tapped Kerik, 49, earlier this month as his nominee for homeland security secretary, but Kerik abruptly withdrew his name Dec. 10 after revealing that he had not paid all required taxes for a family nanny-housekeeper and that the woman may have been in the country illegally.
He has been hit with other allegations as well, including that he had connections with people suspected of doing business with the mob and that he had simultaneous extramarital affairs with two women.
Kerik's nomination became a political embarrassment for Giuliani, a rising star in the GOP who had recommended his friend and business partner to Mr. Bush.
After leaving the police department in 2002, Kerik joined Giuliani Partners, becoming a security consultant and then signing on to help launch the Iraqi police force.
Giuliani Partners has advised business and government agencies on security, leadership and other issues. The consulting firm advised Trinidad in its battle against a rise in kidnappings and murders and was paid $4.3 million by Mexico City officials for advice on reducing crime there.