Former lawyer Le Cong Dinh, who was sentenced to five years in jail for his subversive activities was released on February 6, nearly two years ahead of the schedule.
VnExpress quoted an anonymous source from the criminal verdict enforcement agency as saying that Dinh, 45, had followed prison regulations and was therefore released early.
Earlier, Dinh's jail term had been reduced twice, down to a total of one year, he said, adding that Dinh will remain under surveillance for three years.
Under surveillance, convicts are not allowed to travel out of designated areas, hold certain jobs and must check in regularly with authorities.
In 2010, a Ho Chi Minh court convicted Dinh and three others of attempting to overthrow the government. They were sentenced to between five and 16 years in prison.
Dinh appealed the verdict and a court in the same year refused to decrease his sentence, saying it was already less than the charge mandated because he had demonstrated sincere repentance.
According to Vietnam's Penal Code, attempting to overthrow the government carries a sentence of between 12 years and death.
According to the indictment, Dinh joined the US-based Dang Dan Chu Vietnam (Vietnam Democratic Party) in 2008. Afterward Dinh began disseminating distorted information about Vietnam's government.
Dinh was arrested in June 2009.