Gramm, R-Texas, came in for a wave of criticism this month when he told an interviewer the United States was in a "mental recession" and said America had "sort of become a nation of whiners."
McCain publicly disassociated himself from Gramm's comment and the campaign said Gramm would step aside from his advisory role -- but syndicated columnist Robert Novak reported Friday that Gramm had apologized to McCain for the episode and that Gramm would remain with the campaign as an adviser and as a surrogate for the candidate.
Gramm issued a statement late Friday saying he was leaving the campaign, The Hill reported.
"It is clear to me that Democrats want to attack me rather than debate Sen. McCain on important economic issues facing the country," Gramm said. "That kind of distraction hurts not only Sen. McCain's ability to present concrete programs to deal with the country's problems, it hurts the country."