Prosecutors accused Wendell Nielsen of unlawfully marrying three women besides his legal wife.
His defense attorney argued that "celestial marriages" weren't a violation of state bigamy laws.
The 71-year-old Nielsen was found guilty of three counts of bigamy.
Nielsen is the former president of the fundamentalist church of Jesus Christ of Latter-Day Saints.
He was one of 12 people indicted after a 2008 raid on the polygamist sect's West Texas ranch.