Huynh Thuc Vy, who is currently pregnant, will not have to serve her sentence until her expected child is three years old.
Vy has challenged the government on a range of issues, including the violation of ethnic minority rights in the Central Highlands, the environmental disaster that hit the central coast in 2016, and plans to further restrict internet freedom with a new cyber security law.
However, it was her decision to splash white paint on two national flags during National Day celebrations in September last year that led to her arrest.
She posted a picture of herself on Facebook standing next to the two flags, an apparent attempt to draw attention to her campaigns by directly challenging the legitimacy of the Communist party.
She later told foreign media that she saw the red flag with yellow star as a symbol of repression and of dictatorial government.
Vy was held under house arrest for more than a year before receiving her sentence at a brief trial near her home in the central province of Dak Lak.
The Central Highlands have seen continuing tension between the Communist authorities and local people.
Much of the conflict has focused on religious freedom and the government’s attempts to suppress independent Christian groups which refuse to accept Communist party direction.
Vy said she was not surprised by the sentence and believed it was an attempt by the authorities to drive her out of the country.
Her father served ten years in jail for anti-state activity until his release in 2002.
More than fifty bloggers and other activists have been arrested and sentenced to jail terms this year as the government steps up its drive to silence critics.
Vietnam, however, is not alone in prosecuting citizens who deliberately deface or damage the national flag.
Even some democratic countries, including France, are able to bring criminal prosecutions for such actions.
The flag is particularly sensitive in Vietnam given the country’s history of national division and the Communist party’s insistence that it’s the sole legitimate representative of the Vietnamese people.
Some Vietnamese exile groups continue to brandish the old yellow flag with red lines of the defeated Saigon regime, a gesture seen as subversive and counter-revolutionary by the ruling party.