"I think that you have more credibility if you run for only one office at a time," Paul said.
Paul said he will serve out his term through December 2012, though he acknowledged that he may miss some votes because of the presidential campaign. He said he would continue to provide constituent services.
As for the issues he believes passionately about, including U.S. foreign and economic policy, he said he will always fight for those, whether in public office or not.
"I believe I can continue to do what I have been doing outside of Congress," Paul said of his sometimes controversial political efforts. "I was ready for a change."
The former obstetrician has served 12 terms in Congress from Texas Congressional District 14, centered on Lake Jackson. He was first elected in 1976 in a special election, but later lost in a general election. He won again in 1978. His mix of Libertarian and Republican politics has prompted many to call him the "intellectual godfather" of the tea party movement.
He is the author of six books on politics and monetary policy. This is his third presidential run.