Former US Senator Rick Santorum has suspended his campaign for the Republican presidential nomination.
He made the announcement this evening in his home state of Pennsylvania, two weeks before the Republican presidential primary there.
His decision clears a path for the former Governor of Massachusetts, Mitt Romney, to become the Republican Party nominee.
"While this presidential race is over for me and we will suspend our campaign effective today, we are not done fighting," Mr Santorum told a news conference in Gettysburg, Pennsylvania, saying he will work to help defeat Democratic President Barack Obama in November's election.
Mr Santorum made no mention of Mr Romney, and stressed that he had gone farther than anyone expected, competing "against all odds".
The 53-year-old was a virtual unknown when he first threw his hat into the ring in June last year to be the Republican Party's nominee.
Despite being written off early on, Mr Santorum built his campaign state-by-state.
But he faced the ignominious prospect of possible defeat in his home state of Pennsylvania, which is due to hold its presidential primary on 24 April, after openly declaring on several occasions that it was a "must-win" election contest for his foundering campaign.
His exit today, two weeks ahead of the vote, spares him that fate.
Mr Santorum's pro-life, anti-contraception, anti-gay marriage message has gained traction with heartland evangelicals deeply sceptical of Mr Romney, whom they view as a moderate disguised in conservative clothing.
Yet on the other end of the spectrum, critics saw his radical right-wing views as somewhat scary.
A website called "Santorum exposed" said it was dedicated to "shining a bright light" on what it calls the former senator's "extreme positions."
Mr Santorum, a global warming sceptic, has called Mr Obama "a snob" because he believes all kids should have a college education, and said he wanted "to throw-up" when watching former president John F Kennedy talk about the separation of church and state.
"I don't believe in an America where the separation of church and state is absolute," he told US television recently.
At a campaign stop in Ohio last month, Mr Santorum also hit out at Mr Obama saying the president's "world view" elevated the Earth above man.
"That's what I was talking about - energy: this idea that man is here to serve the Earth, as opposed to husband its resources and be good stewards of the Earth. And I think that is a phony ideal."
Asked to define himself in one word at a recent debate, Santorum replied "courage". That steely resolve, refusing to stray off his message of "Family, Faith and Freedom," has defined his campaign even as it struggled.
A trained lawyer and father-of-seven who has been married to his wife Karen for 21 years, Mr Santorum was first elected to the House of Representatives for Pennsylvania in 1990. He served two terms in the US Senate from 1995 to 2007.
In an intensely personal speech following his early win in Iowa, Mr Santorum described his roots in Pennsylvania's coal country, where his grandfather worked in the mines until he died at 72.
"I knelt next to his coffin. And all I could do - eye level - was look at his hands. They were enormous hands. And all I could think was those hands dug freedom for me."
Mr Santorum has often spoken of his seriously ill youngest daughter, Isabella Maria, who suffers from a genetic disorder, trisomy 18 - or Edwards syndrome - which results in severe disabilities and abnormalities.
He had to break away from the campaign trial in January and again over the weekend to be by her bedside as the three-year-old recovered from treatment.
He has also tearfully recounted a family tragedy in 1996 when a son died hours after being born prematurely. He and his wife spent the night with the body and brought it home to show to their other children before burying it.
"Ask me what motivates me, it's been the dignity of every human life," Mr Santorum said in his Iowa speech.
