Jon Huntsman, the former ambassador to China who tried to avoid partisan attacks during a presidential campaign that never connected with Republican primary voters, is to withdraw from the race for the nomination, campaign officials said.
Mr Huntsman will endorse front-runner Mitt Romney at an event in South Carolina, where the next primary will be held, the officials said.
Mr Huntsman believes Mr Romney is the best candidate to beat President Barack Obama in November, they said.
The former Utah governor placed third in last week's New Hampshire primary despite devoting most 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".
Word of the Huntsman withdrawal came on the same day The State, South Carolina's largest newspaper, endorsed him for president.
The endorsement said there were "two sensible, experienced grown-ups in the race", referring to Mr Romney and Mr Huntsman.
But it said Mr Huntsman "is more principled, has a far more impressive resume and offers a significantly more important message".