A Utah judge has been widely criticised after describing a rapist an "extraordinarily good man" during his sentencing hearing.

Judge Thomas Low sentenced Mormon bishop Keith Robert Vallejo to life in prison after a jury found him guilty of ten counts of sexual abuse and one of rape.

"The court has no doubt that Mr Vallejo is an extraordinarily good man," Low said, while handing down the sentence in front of one of the victims. "But great men sometimes do bad things."

Julia Kirby, a 23-year-old victim of Vallejo's assault, told the Associated Press she planned to file an official complaint against Low over his comments.

"He only cared about the person he was convicting, and I think that is really kind of despicable," she said.

The prosecutor in the case, Ryan McBride, said Low's comments about the defendant were inappropriate.

"I don't think it's wrong to acknowledge the good things that someone has done in their lives," McBride told the AP. "But I think whenever you do that in a case like this, you've also got to say, 'But it doesn't excuse what you've done.'"

McBride said more than 50 people who knew Vallejo had written letters of support and mentioned his good qualities.

An LGBT rights group based in Utah, Restore our Humanity, has said it plans to file a complaint with the state's Judicial Conduct Commission against Low, citing bias and a lack of independence as reasons the judge should be removed from the bench.

The group's Mark Lawrence said Low's remarks were the kind that "make it difficult for victims and survivors of sexual abuse to come forward".