By Agence France-Presse
William Nguyen, 32, was taken into custody on June 10 by plainclothes police during mass protests in Ho Chi Minh City against proposed special economic zones.
The demonstrations quickly spun out of control when rioters set cars on fire and damaged government property in actions against the proposal to grant foreign investors 99-year land leases on the SEZs.
The Texas-born Yale graduate was accused of trying to damage a fence and flip over police vehicles on the main road to the airport.
At a half-day trial at Ho Chi Minh City's people's court Friday, Nguyen was found guilty of a public disorder offence and told to leave the country.
"The People's Court of Ho Chi Minh City applied the deportation order against Nguyen William Anh," a court clerk told AFP without providing further details.
In a televised report aired by local state-run HTV some days after his arrest, Nguyen confessed to his role and promised "not to join any anti-state activities any more."
According to Nguyen's family and friends, he was only there to celebrate the right to free assembly.
"Will is free," his sister Victoria Nguyen told AFP on Friday.
Six Vietnamese have been jailed over the protests.
To calm tensions the communist government delayed the proposed bill, which stirred fears that Vietnamese land could be handed over to Chinese firms on soft terms.
Communist Vietnam still bans public protest.
Vietnam's latest deadly protests erupted in 2014 when Beijing moved an oil rig into waters claimed by Vietnam.
Violent riots destroyed several foreign invested facilities and killed several Chinese nationals.