Court witnesses said Smart and her mother smiled when the guilty verdict was read.
"It is possible to move on after something terrible has happened, and we can speak out and we will be heard," Smart told members of the media outside the courthouse. "
Defense lawyers did not dispute that Mitchell kidnapped Smart, but they wanted him to be found not guilty by reason of insanity. Jurors rejected that argument. Such a verdict would have sent him to a prison mental hospital.
During the five-week trial, Smart testified that she was forced to enter a polygamous marriage with Mitchell, endured near-daily rapes and was forced to use drugs and alcohol.
Smart was 14 years old when she was abducted from her home at knifepoint on June 5, 2002. She was found nine months later.
"I think the hardest part of coming in here was worrying about Elizabeth having to testify," said Smart's father, Ed. "As a father, I was so grateful for her to say what she had to say and put that behind her."
The U.S. attorney on the case applauded Smart for all her help in this trial.
"That young woman had the ability and the willingness to recall the graphic details of her nine-month captivity. And she did it with candor and clarity and a truthfulness that I think moved all of us," said attorney Carlie Christensen.
The shackled Mitchell sat singing about Jesus Christ on the cross throughout the reading of the verdicts Friday morning. He had to be removed several times from the courtroom for his loud singing. Prosecutors said it was all an act.
Mitchell's ex-stepdaughter Rebecca Woodridge, who says she was molested by him but has since forgiven him due to his mental state, spoke outside the courthouse Friday.
She said she is extremely disappointed by the verdict and that God had commanded Mitchell to commit these crimes.
"He is not in his right mind," Woodridge said. "Whether he was responsible for what he did to me, I don't think he really understood 100 percent how wrong it was."
Mitchell's estranged wife, who assisted with Smart's kidnapping, is serving 15 years in federal prison.
Mitchell could face up to life in prison when he is sentenced next May 25.
The Associated Press contributed to this report.