Colombian President Juan Manuel Santos and Marxist rebel leader Timochenko used a pen made from a bullet on Monday to sign an accord ending a half-century war that killed a quarter of a million people.
After four years of peace talks in Cuba, Santos, 65, and Timochenko - the nom de guerre for 57-year-old revolutionary Rodrigo Londono - shook hands on Colombian soil for the first time in front of hundreds of dignitaries.
One man waved a large Colombian flag that had an extra white stripe in homage to the peace deal.
The end of Latin America's longest-running war will turn the FARC guerrillas into a political party fighting at the ballot box instead of the battlefield they have occupied since 1964.
Guests at the ceremony in the Caribbean coastal city of Cartagena were asked to wear white and included United Nations Secretary-General Ban Ki-moon, Cuban President Raul Castro and U.S. Secretary of State John Kerry.