The leader of the Kazakh opposition party Algha (Forward), Vladimir Kozlov, said his early release on parole was made possible by the involvement of the European Union.
Addressing reporters in Almaty on August 22, three days after his release from jail, Kozlov said the EU and the European Parliament had helped him "remain a human being" while in jail.
Kozlov said despite some parole restrictions he would "continue doing everything to be useful for people."
Kozlov was arrested in January 2012 for his role in a mass strike by oil workers in the western city of Zhanaozen that ended in violence in December 2011.
During the unrest, police shot dead at least 16 people. More than 100 people were also injured.
In October 2012, Kozlov was found guilty of inciting social discord and sentenced to 7 1/2 years in jail.
EU officials and rights organizations had called on the Kazakh government to release Kozlov.