Former math lecturer Pham Minh Hoang was put on a plane to Paris late Saturday, weeks after his Vietnamese citizenship was revoked -- a rare move that has sparked outrage among critics of the communist government who accuse it of quashing dissent by any means available.
"I am very sad," Hoang told AFP by phone after his arrival in Paris.
"I tried to do the best I can but today I lost the battle, I lost the war," he said, adding he would continue pushing for democracy in Vietnam.
Hoang said police surrounded his house on Friday night and took him away with no prior warning.
He met French consular officials and a lawyer before his deportation but was unable to say goodbye to his wife Le Thi Kieu Oanh.
"I feel totally defeated... when my husband left, I couldn't say any farewell words, I also feel very angry," Oanh told AFP.
After speaking to Hoang on arrival in France, Oanh said she was at least reassured he no longer faced political persecution.
While authoritarian Vietnam routinely jails critics of its regime, 62-year-old Hoang is the first Vietnam-based dissident to have his citizenship revoked in recent history.
Human Rights Watch called the revocation an "unprecedented and shocking action".
"(It) crosses many human rights red lines on freedom of expression, right to nationality and exercise of basic civil and political freedoms," HRW said in its statement.
Hoang found out his Vietnamese citizenship had been stripped early this month after he received a letter dated May 17 and signed by the president, a decision he unsuccessfully tried to appeal.
He was convicted in 2011 of attempted subversion for publishing a series of articles which prosecutors said were aimed at overthrowing the government.
Hoang was released from jail after 17 months and ordered to serve three years of house arrest. He continued to post articles critical of the government on social media following his release from prison.
Hoang moved to France in 1973 and lived there for 27 years before returning to Vietnam to work as a mathematics lecturer at the Polytechnic University of Ho Chi Minh City.
He told AFP this month he had to stay in Vietnam to care for his disabled brother and elderly mother in law, whom his wife will now look after.