Hueseyin A. was found guilty of being the ring leader of the PKK in Germany - which is considered a terrorist organization in the European Union - from mid 2007 until April last year.
The Kurdish Turk had been living in Germany under the alias Hueseyin Colak, the court said.
Federal prosecutors in the three-month case had been seeking a four-year term for the 48-year-old.
Hueseyin A. was also found to have threatened to kill a 21-year-old Kurd unless she aborted a child fathered by a Stuttgart PKK official.
He was arrested in the western German city of Detmold in July last year. The PKK has been outlawed in Germany as a criminal gang because of its violence against renegade former members.
Editor: Neil King