Michele Bachmann has ended her US presidential campaign, becoming the first Republican candidate to exit the race after a disappointing finish in Iowa's first-in-the-nation caucuses.

Bachmann, an Iowa native who had invested most of her resources in the state, earned just five per cent of the vote for a sixth place finish in the state and failed to win a single county.

"Last night the people of Iowa spoke with a very clear voice, and so I have decided to stand aside," she said at a news conference in Iowa on Wednesday.

Bachmann stressed the importance of uniting the party behind the eventual nominee and vowed to continue to fight President Barack Obama and what she called his "socialist policies".