"I am running for president to return our country to the principles of liberty and limited government," the Republican wrote on his website.
Paul is scheduled to kick off his campaign with a rally in his hometown of Louisville, Kentucky, on Tuesday and he will also take questions via social media.
The one-term senator is expecting to find his strongest support from his home state, but is expected to hold rallies around the country in the next few days, including New Hampshire, South Carolina and Nevada.
Along with 47 Senate Republicans, Paul signed an open letter to Iran’s leaders saying that any nuclear deal could be revoked by Congress.
Prior to that, he voiced his support for diplomacy in negotiating with Iran, breaking with fellow Republican Sens. Marco Rubio and Ted Cruz. "Are you ready to send ground troops into Iran? Are you ready to bomb them? Are you ready to send in 100,000 troops? I'm a big fan of diplomatic options as long as we can," he said during a presidential forum in January.
Paul is the second Republican to declare his candidacy for president. Sen. Cruz from Texas announced his intention last month.