Zhou Shifeng, a lawyer in Beijing, was jailed for seven years on Thursday by Tianjin No 2 Intermediate People's Court for subverting State power.
Zhou said that he accepted the verdict and would not appeal to a higher court.
The 52-year-old former director of Beijing Fengrui Law Firm played a major role in a group of activists who attempted to manipulate public opinion and damage national security by spreading subversive thoughts, the verdict said.
Thursday's trial received a large amount of public attention from both home and abroad.
The verdict said that Zhou colluded with Hu Shigen, the leader of an illegal organization that broadcast subversive ideas, and activists Zhai Yanmin and Li Heping.
They used the law firm as a platform to encourage lawyers to highlight sensitive cases and hired protesters to disturb the judicial system, according to the verdict.
Zhou also asked administrative officers in the law firm to post anti-government comments online to stir up public sentiment, the court said.
Hu and Zhai were sentenced to seven-and-a-half years and three years in jail with a four-year reprieve, respectively, earlier this week.
Li is being prosecuted in a separate case.