Leon Andres Montes, 24, who was kidnapped in July 2012 in the northern town of Amalfi, was released to the Red Cross on Sunday, Colombia Reports said.
ELN spokesperson Dario Ramirez previously said the group kidnapped Montes because the Chilean forestry company he worked for, Compania Agricola de la Sierra, had destructive social and environmental practices.
The rebel group, which is the second largest in Colombia, also accused the Chilean company of taking over 100 parcels of land, planting non-native trees and displacing the farmers who lived there.
Montes' parents told Caracol Radio that they believe their son's release may help further peace talks between the government and ELN.
"It will be an opportunity for us and for the country, I hope it's the beginning of a better world, not only for our family, but for Colombia," said Isabel Ceballos, Montes' mother.
ELN is the Spanish acronym for the National Liberation Army, a relatively small Marxist group.