Rand Paul has decided to drop out of the White House race after a disappointing fifth place finish in the Iowa caucuses.
The Kentucky senator often clashed with his Republican rivals over their hawkish views on foreign policy and their support of government surveillance.
Rand Paul ended his bid in part to focus on his re-election to the Senate.
He is seen as representing the Libertarian wing of the party, which promotes individual rights and privacy.
“Across the country thousands upon thousands of people flocked to our message of limited government, privacy, criminal justice reform and a reasonable foreign policy,” he said.
“Although, today I will suspend my campaign for president, the fight is far from over.”
Rand Paul, an ophthalmologist, represents Kentucky in the Senate and is the son of former Congressman Ron Paul, who ran for president several times.
He has said in the past he is the right candidate to “stand up to both the right and the left”.
In 2015, a Time magazine cover labeled Rand Paul “the most interesting man in politics”.
There are now 10 Republicans left in the White House race, down from the original 17.
Rand Paul, 52, hoped to gain the attention of young people hoping for change but was ultimately overshadowed by billionaire businessman Donald Trump.
He is known for holding up the Senate floor for nearly 13 hours to delay the nomination of John Brennan as CIA director because of his opposition to the Obama administration’s use of drone strikes against terrorists.
He also was criticized last year when he said vaccines could give children “profound mental disorders”. He later said his children are immunized.
Rand Paul was passionate about criminal justice reform, saying the US needs to “break the cycle of incarceration for non-violent ex-offenders”.
He was praised for level-headed debate performances, but ultimately was hurt by his non-interventionist polices after terrorist attacks in San Bernardino, California and Paris.
Rand Paul had trouble raising money for his campaign, as well, not attracting wealthy donors flocking to candidates like Marco Rubio, Jeb Bush and Ted Cruz.
With such a large field of candidates, underperforming Republican candidates are under increasing pressure to drop out of the race.
Former Governor of Arkansas Mike Huckabee dropped out on February 2 as votes were being cast in Iowa.
Republican and Democrat presidential hopefuls have arrived in New Hampshire ahead of the next vote.
Iowa caucuses on February 2 were won by Senator Ted Cruz for the Republicans and Hillary Clinton for the Democrats.
Ted Cruz prevailed despite trailing in opinion polls while Hillary Clinton beat Senator Bernie Sanders by just 0.2%.
New Hampshire is seen as a quite different challenge for the parties.
The state’s more moderate and less religious electorate may prove a tougher nut for Ted Cruz to crack in the primaries it is due to hold on February 9.
Long-time frontrunner Donald Trump is expected to do much better than in Iowa, which held the nation’s first vote.
On the Democrat side, Bernie Sanders is seen as having a home advantage in New Hampshire over Hillary Clinton, being a senator of the neighboring state of Vermont.
The state-by-state voting will culminate in conventions in July, at which the two parties will confirm their choice of candidate to succeed Barack Obama, the Democratic president who is standing down after two terms in office.
Even before Hillary Clinton’s narrow victory was announced officially, Bernie Sanders was up at 05:00 and aboard a flatbed lorry, being greeted by supporters in the New Hampshire town of Bow.
Telling the crowd that his campaign had “astounded the world” in Iowa, Bernie Sanders promised it would “astound the world again” in New Hampshire.
Hillary Clinton is due to address a crowd at a sports stadium in Nashua.
Final results show Hillary Clinton took 49.8% in Iowa to Bernie Sanders’ 49.6%.
Ted Cruz took 26% of the Republican vote to 23% for Donald Trump, but Senator Marco Rubio finished a surprisingly strong third, just slightly behind.
The Texas senator declared his win a “victory for courageous conservatives”.
Many mainstream Republicans favor Marco Rubio, fearful that Ted Cruz and Donald Trump may alienate voters with their combative style.