The new deal does not modify a controversial part of the previous accord that gives the FARC 10 congressional seats through 2026.
Colombia's government and Revolutionary Armed Forces of Colombia (FARC) rebels announced on Saturday a revised peace deal to end 52 years of armed conflict, after voters rejected a previous peace accord in a referendum.
The government and leftist FARC group, which have been holding talks in Havana for four years, said they had incorporated proposals from the opposition, religious leaders and others.
President Juan Manuel Santos hopes to unite the divided nation behind the new deal after the peace process was endangered by its rejection in the October referendum.
Colombian voters were deeply split, with many worrying the FARC would not be punished for crimes, and others hopeful the deal would cement an end to violence.
"We have reached a new final agreement to end the armed conflict, which incorporates changes, clarifications and some new contributions from various social groups," said a joint statement read out by diplomats from Cuba and Norway, the peace process guarantors.
"Building a stable, lasting peace must be the shared commitment of all Colombians, and one that helps polarisation be overcome while including all social and political voices," the statement added.
"We call upon all Colombia and the international community ... to back this new accord and its quick implementation so as to leave the tragedy of war in the past," the two sides said in a statement. "Peace cannot wait anymore."
Colombia's Nobel prize-winning President Juan Manuel Santos stressed: "It is a better agreement."
The new accord was fine-tuned after the groups that opposed the original deal submitted proposed changes as starting points for negotiations.
"We are convinced that this documents highlights viable and possible paths" to end the conflict, said the government's lead negotiator Humberto de la Calle.
"The tweaks and clarifications we have made do not undermine the issues we agreed on, which shaped the first peace deal," he said.
An upbeat chief rebel negotiator Ivan Marquez said "the only thing the new accord needs now is to be put into effect."
At the moment, neither side has made any mention of whether a referendum would be held for the new peace deal.
The US hailed the agreement, and pledged continuing support of a peace plan under which the guerrillas would demobilise and become a political party.
FARC and Santos' government had been meeting since October 22 to try to rescue a peace deal that has taken four years to negotiate.
The new deal will not modify a controversial part of the accord that gives the FARC 10 congressional seats through 2026, or prevent rebel leaders from eventually being elected to political posts.
However, the accord will not be integrated into Colombia's constitution, and the FARC will be required to present a complete inventory of its assets, which are destined for victim compensation, Santos said in a televised address.
The modified accord also takes foreign magistrates off special peace tribunals, although there will be foreign observers, and stipulates the FARC must turn in exhaustive information about its involvement in the drug trade.
The new deal limits the work of the special tribunals to 10 years and requires any investigations be opened within the first two years.
An opposition suggestion that FARC leaders not be allowed to run for office once they have finished their alternative sentences was not debated with the rebels, Santos said.
"It is very important Colombians understand that the reason for all peace processes in the world is precisely that rebels lay down arms and can participate in legal politics," Santos said.
He further said the deal would ensure FARC rebels sentenced by the special court will be restricted to certain areas, living arrangements and work hours.
Former President Alvaro Uribe, who led the opposition against the original accord, was not pleased with the modified deal, sources said.
Uribe, who met with Santos on Saturday, said his camp and victims should be able to study the new deal before it is implemented.
"I have asked the president that the texts they announce in Havana not be definitive," he said in a statement, adding that the opposition might want to make further tweaks.
Meanwhile, talks with the smaller ELN (National Liberation Army) have been on hold over government demands it first free all hostages.
Santos's government had been due to open peace talks with the ELN, Colombia's second-largest rebel group, on October 27.
Founded in 1964, the FARC and the ELN are the last two leftist guerrilla groups involved in a messy, multi-sided conflict that has killed more than 260,000 people, left seven million displaced and 45,000 more people missing.