Paul grew up on his family's dairy farm just outside Pittsburgh. He earned a bachelor's degree in biology from Gettysburg College in 1957 and a medical degree from Duke University, in Durham, N.C., in 1961. He later served as a flight surgeon for the U.S. Air Force (1963–65) and the Air National Guard (1965–68). In 1968 Paul moved to Brazoria county, Texas, where he established a successful practice in obstetrics and gynecology.

Paul was inspired to enter politics in 1971 when Pres. Richard M. Nixon (Nixon, Richard M.) abolished the Bretton Woods (Bretton Woods Conference) exchange system. Paul believed that the abandonment of the last vestiges of the gold standard would lead to financial ruin for the United States. Though he was unsuccessful in his initial run for the U.S. House of Representatives in 1974, his opponent resigned before completing his term, and Paul won a special election to complete it. He lost the seat in the subsequent general election, only to regain it two years later. He chose not to seek reelection in 1984 and instead campaigned—unsuccessfully—for the Republican nomination for U.S. Senate. He broke from the Republican Party to run as a Libertarian in the 1988 presidential election, ultimately winning more than 430,000 votes. He returned to the U.S. House of Representatives as a Republican in 1997, though his votes were often at variance with the majority of his party; for example, in the early 2000s he voted against authorizing the Iraq War and the USA Patriot Act.

Paul's presidential campaign platform remained libertarian in spirit. It focused on free-market economics, a radical reduction in the size of government, increased privacy protections for individuals, and a reduction of U.S. participation in international organizations. Having claimed only a handful of delegates, he ended his bid for the White House in June 2008 and launched Campaign for Liberty, a political action committee. His views are outlined in Freedom Under Siege (1987), A Foreign Policy of Freedom (2007), and The Revolution: A Manifesto (2008).