Republican Rand Paul officially announced on his website on 7 April that he will run for US president in 2016, hours before an event in his home state of Kentucky where he is expected to formally launch the campaign.
"I am running for president to return our country to the principles of liberty and limited government," he said in a posting at www.randpaul.com.
Paul is expected to announce his candidacy at what is described by his PAC as "a very special rally" scheduled for 11.30am at a hotel in Louisville, Kentucky's largest city.
The firebrand who wants to scale back the authority of the Federal Reserve has been quietly courting Wall Street donors. The anti-war agitator who mounted a 13-hour filibuster to call attention to the United States' use of drones recently proposed a boost to military spending.
His expected announcement on Tuesday will make him the second major Republican figure to announce presidential ambitions for 2016 - after Senator Ted Cruz of Texas. The field is expected to be crowded, and candidates will be competing hard for constituencies ranging from the Christian right to traditional Wall Street Republicans.
On many issues, Paul's positions aren't different from mainstream Republicans. He opposes Obamacare and abortion and favours cutting taxes and spending. But his criticism of the Federal Reserve has spooked many in the party's business-friendly wing, and his proposal to balance the federal budget within five years is dramatic even by the standards of the anti-spending Republican Party.
Paul was active in libertarian circles before he decided to run for an open US Senate seat in Kentucky in 2009. He became one of the best known faces of the insurgent Tea Party movement when he upset a favoured candidate in the Republican primary a year later and went on to win the election.