Wanda Barzee, 72, left the Utah state prison in the Salt Lake City suburb of Draper, spokeswoman Kaitlin Felsted said in a statement that did not provide details about Barzee's destination.
Barzee's release followed a surprise announcement last week that Utah authorities had miscalculated the amount of time she should serve in prison. Barzee was previously scheduled to be released in 2024.
Smart, now 30, said last week that she was shocked and disappointed and hopes Barzee will be closely watched and given treatment.
Barzee will be under federal supervision for five years. If she violates terms that include mental health treatment and an order not to contact Smart's family, she could go back to prison.
Smart recalled some of the horrors she experienced as a 14-year-old when she was snatched from her Salt Lake City home in 2002 by Barzee's then-husband, street preacher Brian David Mitchell. Mitchell came in through an open kitchen window in a kidnapping that triggered waves of fear around the country.
Smart said at a news conference last week that Barzee saw her as a slave during the nine months she was held by the couple and encouraged Mitchell to rape her.
"So do I believe she's dangerous? Yes," Smart said.
Smart was found while walking with Barzee and Mitchell on a street in the suburb of Sandy by people who recognized the couple from media reports.
Mitchell is serving a life sentence after being convicted of kidnapping and raping Smart.
Barzee was treated at the Utah State Hospital for about five years following her arrest. She testified in 2010 against Mitchell and was given a plea deal on state and federal charges. She was transferred to the Utah state prison in April 2016 after finishing a federal sentence in Texas.
The Utah Board of Pardons and Parole had set a January 2024 release date after Barzee failed to attend her own parole hearing in June, but her attorney questioned whether that included time she had served in a federal prison. The board decided last week that she had served her sentence.
Barzee's attorney, Scott Williams, has said his client has been diagnosed with several mental illnesses, but he's not concerned about her being a danger to the community.
Federal agents have found a place for Barzee to live when she starts her five-year supervised release, said Eric Anderson, deputy chief U.S. probation officer for Utah. He declined to say whether she will be in a private home or a facility but that she "will not be homeless."
One of Barzee's nieces, Tina Mace, said her aunt's testimony against Mitchell seemed like a turning point but that her mental state appears to have changed in prison. Mace said she's unaware of any family members that would take in Barzee.
Smart, now a married mother and activist for victims' rights, posted on Instagram over the weekend that she's fearful of Barzee and has taken precautions but said she refuses to let her release disrupt the life she's built.
"I have spent the last 15 years rebuilding and moving forward with my life, having a family, and pursuing my goals," Smart wrote. "I lived in absolute fear and terror for nine months, no matter the outcome I will not do so again."