Nguyen Van Hai publishes his reporting through a blog, Dieu Cay ("Peasant's Pipe"), which also serves as his pen name. He is a founding member of the Club for Free Journalists, created in September 2007. In 2008, he participated in as well as reported on Vietnamese protests against the Beijing Olympics following a China-Vietnam maritime dispute.
Hai was arrested on 20 April 2008 in Ho Chi Minh City, and his computers and files were confiscated. He was then charged with tax evasion and sentenced to thirty months' imprisonment.
He was scheduled for release in October 2010, but on the day of his release, his sentence was extended "pending further investigation". His home was allegedly also raided and his wife Duong Thi Tan beaten. On 5 July 2011, Duong Thi Tan was informed that Nguyen Van Hai had lost one of his arms due to an injury sustained in prison.
In April 2012, he was brought to an additional trial for "spreading anti-government propaganda" along with bloggers Ta Phong Tan and Phan Thanh Hai. Nguyen Van Hai pleaded not guilty. According to the state newspaper Thanh Nien, Nguyen Van Hai and Phan Thanh Hai were also believed to have attended a training seminar sponsored by the overseas opposition party Viet Tan.
Human Rights Watch condemned the arrests and called for the immediate release of the three bloggers. In 2009, the group awarded Nguyen Van Hai its Hellman-Hammett Award "for writers who have suffered persecution as a result of their writings". Amnesty International designated him a prisoner of conscience, expressing concern at reports of his weight loss and deteriorating health.
On 6 March 2012, former U.S. Representative Joseph Cao organized a Vietnamese-American lobbying effort for Hai, Nguyen Van Ly, Nguyen Dan Que, and other Vietnamese political prisoners, calling on the administration of President Barack Obama and the U.S. Congress to take a stronger stand on their behalf. In April, Civil Rights Defenders named him its Human Rights Defender of the Month. On 17 April, a US State Department spokeswoman called on Vietnam to release Nguyen Van Hai and the other bloggers, stating that the three had "done nothing more than exercise their universally recognized rights to freedom of expression". U.S. President Barack Obama said in May 2012 that "we must not forget journalists like blogger Dieu Cay, whose 2008 arrest coincided with a mass crackdown on citizen journalism in Vietnam"
In 2013, he was awarded the International Press Freedom Award of the New York-based Committee to Protect Journalists.
In September 2012, in a one-day trial of three dissidents including Ta Phong Tan and Phan Thanh Hai, Nguyen Van Hai received the harshest sentence of twelve years in prison. The Economist described the session as looking "very much like an old-fashioned Soviet-style show trial". Prosecutors stated that the three had "distorted the truth about State and Party, created anxiety among citizens and supported schemes to overthrow the government", while the court found that they were "seriously affecting national security and the image of the country in the global arena." Phan Thanh Hai, who had pleaded guilty, was sentenced to four years' imprisonment, and Ta Phong Tan to ten years.
Nguyen Van Hai's former wife, Duong Thi Tan, stated that police detained her and her son for several hours to prevent them from attending the trial.
The sentences were upheld by an appeals court on 28 December 2012.
On 21 October 2014, Hai was released by the Vietnamese authorities and sent to the United States.