Nguyen Van Hai, one of Vietnam's most prominent bloggers, has chosen to move to the United States and was expected to arrive later in the day, State Department deputy spokeswoman Marie Harf said.
Hai, alias Dieu Cay, was sentenced to 12 years in September 2012 by a court in southern Vietnam on charges of "anti-state propaganda." Two other bloggers received jail terms of 10 years and four years.
"We welcome the decision by Vietnamese authorities to release this prisoner of conscience," Harf told reporters.
In May 2012, Obama said that the world "must not forget (journalists) like blogger Dieu Cay, whose 2008 arrest coincided with a mass crackdown on citizen journalism in Vietnam."
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Hai, who went on hunger strike at least twice to protest his jailing, has been in detention since September 2008, when he was sentenced to two-and-a-half years for tax fraud.
The charges of conducting propaganda against Vietnam's one-party communist state are routinely used to prosecute dissidents in a country that rights groups say is conducting a growing crackdown against freedom of expression.
Hai's release comes only weeks after the US said it was partially lifting a 40-year ban on arms sales to Vietnam, partly because of an improvement in human rights.