Rodrigo Londono, the Farc leader, pronounced the "opening of a new era" for Colombia and for the Farc as a peaceful political movement.
"Goodbye to war! Welcome, peace!" he said.
It has been a process marked by setbacks, including the rejection of the deal in a referendum last year, forcing hasty revisions before it was rubber-stamped by Parliament.
Demobilisation has been slow, with complaints from guerrillas that the Government had failed to fulfil its promises.
But yesterday, the UN said it had received all 7132 individual weapons registered by the Farc. It had also verified 77 stockpiles and destroyed explosives and ammunition.
However, many Colombians fear the days of terror are not yet over. In some regions, the withdrawal of the Farc has heralded an upsurge in violence as para-militaries and other guerrilla groups, such as the ELN, battle for control of territory.
The drug trade has exploded, with cocaine production more than doubling in the past three years.