He has proven to be a thorn in the side of many of his fellow Republicans, openly challenging them on issues such as government surveillance, drone policies and sanctions on Iran and Cuba.
He has also questioned the size of the US military and proposed relaxing drug laws that lock up offenders at a high cost for tax payers.
It is not clear how successful Mr Paul will be amongst mainstream Republican supporters.
His father, former member of the US House of Representatives Ron Paul, ran several unsuccessful presidential campaigns that had strong appeal to libertarians who favour limited government and lower taxes.
Mr Paul is expected, however, to run a very tech-savvy campaign that could create appeal to new Republican demographics, like young voters.
Indeed, the campaign's official announcement first came in a post on his website several hours before he appeared on stage in Louisville, Kentucky.
"I am running for president to return our country to the principles of liberty and limited government," he said in
the online message.
He joins Senator Ted Cruz as the two most prominent declared candidates.
He could face up to 20 other fellow Republicans doing battle for the nomination, including former Florida Governor Jeb Bush and Wisconsin Governor Scott Walker, both of whom are expected to enter the race soon.
