The 34-year-old "brainwashed" dozens of people aged between 14 and 30, according to the public prosecutor, and recruited a number of them to fight for the jihadist organisation in Syria.
A court in the southern city of Graz found the preacher, who goes by the name of Ebu Tejma, guilty of belonging to a terrorist organisation and of inciting terrorist attacks following a trial that has been running since February.
Tejma fled from Bosnia to Vienna following the break-up of Yugoslavia and preached in various Austrian and southern German cities, becoming a "key figure" in pushing IS propaganda, the prosecution said.
He was arrested during a far-reaching crackdown on Austrian jihadist networks in 2014 and denies the charges against him.
A second accused was sentenced to 10 years for his involvement in recruiting fighters, as well as taking part in IS attacks in Syria.
Several trials are currently under way in Austria for involvement in or incitement to jihad.
Authorities suspect some 250 people of jihad-linked activities, the majority of them from Chechnya or Bosnia. At least 40 people who travelled from Austria have died fighting alongside ISIS, according to the interior ministry.