Debbie Vincent, a 52-year-old former soldier, was found guilty last month for her part in a conspiracy to blackmail British-based Huntingdon Life Sciences (HLS).
Vincent became the public face of Stop Huntingdon Animal Cruelty (SHAC) after seven members of the group were jailed for a total of 50 years in 2009 for their role in the campaign.
Members of the group falsely accused HLS staff members of being paedophiles, sent them hoax bombs and sanitary towels claimed to be infected with AIDS, and caused criminal damage to their cars and homes.
In May 2009, activists dug up a grave in Switzerland and removed an urn containing the ashes of the mother of Daniel Vasella, the then-chairman of Swiss pharmaceutical giant Novartis, one of HLS' suppliers.
Sentencing Vincent at Winchester Crown Court in southeast England, judge Keith Cutler said: "It is difficult for a judge to calculate the repugnance felt by society to such appalling acts. Nothing at all could justify such attacks."
He added: "You express no shred of remorse or condemnation for the incidents of extreme terror and desecration which have been caused."
A group of Vincent's supporters held placards outside the court reading "No Excuse for Animal Abuse" and "Against Animal Testing and State Repression".
One of the group, Adrian Shaw, 26, claimed the sentence was aimed at dissuading animal rights protesters who operate within the law.
"We are disappointed at the sentence and in the entire legal process and how it is criminalising above-ground animal rights protesters," he told AFP.
He said Vincent had been made a scapegoat because state prosecutors had accepted that she was not present at any of the incidents across Europe.
"She has put herself forward as the public face of SHAC and she has been scapegoated to try to dissuade other people from engaging in lawful activity," he said.