Xu Zhiyong, 40, who campaigned for children's rights and against corruption last year, was found guilty of "gathering a crowd to disturb public order" by a Beijing court.
Rights groups have criticised Chinese President Xi Jinping, who pledged to fight corruption over the prosecution of Xu, BBC reported.
The case relates to public gatherings held last year by members of the anti-corruption New Citizens Movement, which Xu helped to establish. The group, during their campaign, demanded that ruling Communist Party of China leaders declare their assets.
In his closing statement delivered to the court, Xu denied the charges. "We did nothing to disrupt public order, we were merely exercising our freedom of expression as provided for by the constitution," he said.
The activist was arrested in July 2013, and the trial began this week.
Xu's sentencing drew widespread criticism, with the United States saying it was "deeply disappointed" and sought his immediate release.
"We call on the Chinese authorities to release Xu and other political prisoners immediately, cease restrictions on their freedom of movement, and guarantee them the protections and freedoms to which they are entitled under China's international human rights commitments," US State Department spokeswoman Jen Psaki said in a statement.
Amnesty International described the verdict as "shameful" and Human Rights Watch said convicting Xu "makes a mockery" of Chinese President Xi Jinping's crusade against corruption.
European diplomats also called on Chinese authorities to release Xu immediately.
In total 20 to 40 people involved with the New Citizens Movement have been detained since last year, according to members.
Image: Chinese rights advocate Xu Zhiyong speaks during a meeting in Beijing in this handout photo dated March 30, 2013
Photograph: Xiao Guozhen/Handout via Reuters
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