"It's been an incredible honor to run a principled campaign for the White House," Paul said in a statement. "Today, I will end where I began, ready and willing to fight for the cause of liberty.
Paul finished fifth in Monday's Iowa caucuses with 4.5 percent of the vote, behind rivals Ted Cruz, Donald Trump, Marco Rubio and Ben Carson.
Paul campaigned on defending liberty and shrinking the federal government’s influence in the United States and abroad. Paul was seen as a possible mainstream libertarian alternative to his father, the former Texas congressman and presidential candidate Ron Paul.
Since announcing his candidacy on April 7, 2015, in Louisville, Kentucky, Paul was unsuccessful in breaking single digits in national polls. After his disappointing finish in Iowa, it appears Paul began making plans to exit the race.
"Some of the staff found out yesterday, the rest found out this morning," a source close to Paul’s campaign in New Hampshire told ABC News. "Obviously people here at the office are disappointed, but we think his message will continue to resonate with the freedom movement in the Republican Party."
The man who was dubbed “The Most Interesting Man in Politics” by Time magazine in 2014 wasn’t able to capture the electorate’s attention, even in states like New Hampshire where his libertarian positions have broader appeal.
Paul, 53, was one of the earliest and strongest voices against GOP front-runner Trump on or off the debate stage, calling the billionaire real estate mogul from New York everything from a “fake conservative” to a “delusional narcissist.” He even compared Trump to “Gollum,” the antagonist in “The Lord of the Rings.”
Paul’s campaign focused on gaining grassroots momentum among younger, first-time voters and college students.
Back home in Kentucky, Paul will be gearing up for a re-election campaign where he will be facing off against the Democratic mayor of Lexington, Jim Gray.
ABC’s Brad Mielke contributed reporting.