Colombia's second largest rebel group, the ELN, will hold talks with the government next week to discuss the terms of a possible peace process.
Mr Galan was allowed to leave jail to convince the ELN to begin talks
The exploratory meetings will begin on 12 December at an undisclosed location outside Colombia, both announced.
Similar talks held in Havana in 2003 collapsed after failure to agree on a framework for negotiations.
The ELN and the larger Farc have been involved in a 40-year conflict with state forces and right-wing fighters.
The announcement was made following a meeting between the Colombian peace commissioner, Luis Carlos Restrepo, and the ELN leader, Francisco Galan, near the city of Medellin.
Mr Galan is serving a 30-year sentence for rebellion, terrorism and kidnapping.
But the government allowed him to leave jail for three months in September in the hope that he would convince the rebels to begin talks.
The ELN is believed to have 4,000 members and has been active since 1964.
Colombian President Alvaro Uribe has already started a peace process with the country's main right-wing paramilitary group, the AUC, but the terms of this have been strongly criticised by human rights groups.
The Farc has refused to negotiate with the government.