The plebiscite asks for a simple "yes" or "no" on whether Colombians support the accord signed on Monday by President Juan Manuel Santos, who has staked his legacy on peace, and the rebel commander known as Timochenko.
The Revolutionary Armed Forces of Colombia, known as FARC, whose numbers halved to about 7,000 in recent years due to a US-backed military offensive, have agreed to turn in weapons and fight for power at the ballot box instead of with bullets.
After four years of negotiations in Havana, the final agreement was applauded around the world. Recent polls show about two-thirds of voters are likely to ratify it.
Influential former President Alvaro Uribe has led the "no" camp, arguing that rebels should pay for crimes in jail and never be given congressional seats. But most Colombians, including some who see the accord as too soft on the FARC, seem convinced that an imperfect peace is better than more war.
Under the accord, the FARC, which began as a peasant revolt in 1964, can compete in the 2018 presidential and legislative elections and will have 10 unelected congressional seats guaranteed through 2026.
