"Today, we are laying down our weapons", said commander Rodrigo Londono, alias Timochenko, in a speech in the central town of Mesetas, site of one of the group's demobilization camps.
The UN said 7,132 arms have been stored in secure containers and a small number of weapons will remain in the hands of some rebels for security provision at the camps until they are closed on August 1.
The UN team, which has been tasked with verifying that all weapons were handed over, certified 7,132 individual weapons during the ceremony.
In a ceremony which ended the disarmament process, President Juan Manuel Santos said the "peace was real and irreversible".
Lingering memories of the extermination campaign weigh heavily on the guerrillas, many of whom expressed their fears about returning to civilian life without weapons. But the ceremony signaled to the country that the Revolutionary Armed Forces of Colombia, known by its Spanish initials as the FARC, would no longer threaten Colombians as it had for generations.
"The FARC has committed to tell the truth and make reparations", Santos, who won a Nobel Peace Prize for helping forge the accord, said on Twitter.
"It is bad that numerous guerrillas, militia members, supporters or those accused of belonging to our ranks are still in prison six months after the amnesty and pardon law was passed", Timochenko said.
FARC was formed in 1964 as the military wing of Colombia's Communist Party.
The conflict has left at least 260,000 people dead, more than 60,000 missing and seven million displaced.
On that date, the FARC is expected to deliver a list to the government of properties belonging to it to allow victims of the conflict to benefit from the sale and redistribution of the lands.
Undoubtedly, the FARC disarmament marks a crucial step forward in the peace process, but much remains to be done and the hurdles are many. Another insurgent group, the 1,000-member National Liberation Army, or ELN, has resisted the government's calls to negotiate and continues to kidnap and extort and to bomb oil pipelines.
The ELN started talks with the government this year, though it has been blamed for ongoing confrontations with state forces.
Norway, a sponsor of the peace process, cautiously welcomed the disarmament.
A United Nations statement said it had received 7,132 weapons belonging to Revolutionary Armed Forces of Colombia fighters. Like many other places torn by war, residents of the small town voted overwhelmingly for the peace agreement past year though many still harbor doubts as to whether the guerrillas will follow through on their pledge to completely disarm and abandon their involvement in Colombia's flourishing criminal economy.