Li Heping, best known for defending blind lawyer Chen Guangcheng, was found guilty of "subverting state power," the Tianjin Second Intermediate Court said in a post on its verified microblog.
Li stood trial on Tuesday in the port city of Tianjin, close to the nation's capital, where he said he would "obey the judgement and not appeal," the statement said.
"Because the case involved state secrets, our court had a trial not open to the public...The court fully protects the rights of litigation of Li Heping," it added.
A suspended sentence means Li will be released from detention, but will continue to be closely monitored by police, likely at his home.
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Last August, Chinese courts tried six members of the "709" group in quick succession, finding them guilty of serious crimes including "subverting state power" and "endangering national security".
The courts gave prior notice of the hearings -- even if just a few hours in some cases.
According to Chinese law, in most cases a defendant's family members or lawyers must be informed at least three days before a trial.
"The secret trial shows that allegations against Li Heping are groundless and weak," Amnesty International's China researcher Patrick Poon told AFP.
"Otherwise, why didn't the court inform his family properly before trial and only announce its verdict online?"
Li has not had access to a lawyer of his own choosing since he was detained, according to his former attorneys.
His wife could not be reached for comment.
Chinese President Xi Jinping has overseen a tightening of controls on civil society since assuming power in 2012, closing avenues for legal activism that had opened up in recent years.