In a promotional image released by TV network TLC for the reality series "Sister Wives," Kody Brown (center) poses with his wives, from left, Robyn, Christine, Meri and Janelle. George Lange/AP

A federal judge ruled that key parts of Utah's polygamy laws are unconstitutional, handing a legal victory to a polygamist family that stars in the reality TV show "Sister Wives."

U.S. District Court Judge Clark Waddoups said in the Friday ruling (PDF) that the phrase in Utah law that forbids cohabitation with another person was a violation of the First Amendment.

Washington D.C.-based attorney Jonathan Turley has said that Kody Brown and his four wives drew the attention of Utah authorities because of their hit series on TV network TLC. The Brown family filed their lawsuit in July 2011, and fled Utah for Las Vegas last year under the threat of prosecution.

Turley argued the case before Waddoups in January.

Polygamy is illegal in all 50 states, but Utah's law is unique in that a person can be found guilty not just for having two legal marriage licenses, but also for cohabiting with another adult in a marriage-like relationship when they are already legally married to someone else.

State attorneys have used the cohabitation portion of Utah's law to prosecute Utah polygamists for bigamy. It is punishable by up to five years in prison.

Utah is the headquarters state of the Church of Jesus Christ of Latter-day Saints, or Mormons, which abandoned polygamy in 1890 as Utah was seeking statehood. Some sects and breakaway groups, however, follow the early theological doctrine of plural marriage, thought to bring exaltation in heaven.

U.S. District Judge Clark Waddoups ruled that the second aspect is too broad because it bars consenting adults from living together and criminalizes their intimate sexual relationships.

He said the law violates both the First Amendment's clause ensuring religious rights and the Fourteenth Amendment's due process clause designed to ensure liberty.

"The decision affects a far greater range of such relationships than the form of polygamy practiced by the Browns," Turley said in a statement Friday. "It is a victory not for polygamy but privacy in America."

The rest of Utah's bigamy law remains intact under the ruling, so only individuals who fraudulently obtain multiple marriage licenses would be guilty.

Utah officials had sought to have the suit thrown out. They first argued that the Browns couldn't challenge the bigamy law because they hadn't been charged. State attorneys later argued for dismissal because a prosecutor had pledged not to prosecute them for bigamy.

Kody Brown said in a statement Friday that the family was "humbled and grateful" for the ruling.

"While we know that many people do not approve of plural families, it is our family and based on our beliefs," he said. "Just as we respect the personal and religious choices of other families, we hope that in time all of our neighbors and fellow citizens will come to respect our own choices."

Brown, the four women he lives with and their 17 children are members of the Apostolic United Brethren, a Utah-based church that follows plural marriage doctrine.

They fled to Nevada to avoid a bigamy prosecution after authorities launched a probe into their lifestyle.

No charges were ever brought, but Brown and his wives — Meri, Janelle, Christine and Robyn — launched a federal lawsuit in 2011 contending that Utah's ban on multiple marriage partners violated their right to privacy and criminalized their sexual relationships.

Al Jazeera and wire services