Huntsman spokesman Tim Miller tells ABC News that the former ambassador to China was "proud of the race that he ran" but "did not want to stand in the way" of rival Mitt Romney, the current front-runner for the nomination. Huntsman placed third in last week's New Hampshire primary despite devoting much of his campaign resources to the state.
He had already acknowledged that expectations for him in South Carolina's primary this week will be "very low."
ABC News reports that Huntsman plans to endorse Romney at an 11 a.m. press conference Monday in Myrtle Beach.
The Associated Press contributed to this story.