The leader of the largest polygamous religious sect in the U.S. has been found guilty of two counts of sexual assault on a child.

Warren Jeffs, 55, could face more than 100 years in prison for having sex with two underage girls, members of his sect whom he claimed were his brides from "celestial marriages", the Wall Street Journal reports.

He made international headlines when in 2008 police raided his Texan compound and took away 450 children.

The head of a breakaway group of the Mormons, he is viewed by followers as "The Prophet," a man who can converse with God.

He is believed to have arranged several marriages between under-aged girls and middle-aged men.

Texas prosecutors presented a case built on DNA evidence and audiotapes of his sexual encounters, including with a 12-year-old.

He is heard on the tape calling it a "heavenly session."

DNA tests indicated he had fathered a daughter with a 15-year-old girl.

Jeffs is the leader of a sect called the Fundamentalist Church of Jesus Christ of Latter-day Saints, or FLDS, which years ago broke away from the mainstream Mormon church.

It owns a ranch about 45 miles away from San Angelo in the tiny town of Eldorado.

Jeffs defended himself after sacking several attorneys and then sat motionless or not talking through the week-long trial at Tom Green County courthouse in San Angelo.

In what was also a very strange trial, he would also engage in a type of sermon.

At one point, he stood and made a nearly hour long objection to the judge, discoursing on the history of polygamy and religious freedom, WSJ reports.

He read a statement which he said was from God and threatened all involved in the case with disease, Associated Press reports.

Judge Barbara Walther had to endure him standing mostly silent for his 30-minute closing argument and then uttering "I'm at peace", AP reports.

Jeffs is expected to face another trial, on a bigamy charge, later this year, Wall Street Journal reports.

Texas has charged several other men with sexual assault and bigamy.