Cyntoia Brown, jailed as a 16-year-old for murdering her alleged rapist and whose case was championed by US celebrities as a symbol of unfair prison sentencing, has been released from the Tennessee Prison for Women.

Key points: Ms Brown was sentenced to life in prison as a 16-year-old for murdering her alleged rapist

Ms Brown was sentenced to life in prison as a 16-year-old for murdering her alleged rapist Her emancipation was supported by a number of prominent celebrities including Rihanna

Her emancipation was supported by a number of prominent celebrities including Rihanna Ms Brown says she wants to help female victims of sexual abuse and exploitation

Kim Kardashian West, Rihanna, Snoop Dogg and LeBron James and several other US-based celebrities had lobbied for Ms Brown's release, calling her a sex trafficking victim.

"Cyntoia Brown welcome home!!" James tweeted.

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She was granted clemency in January by outgoing governor Bill Haslam, commuting a life sentence for murdering 43-year-old Nashville real estate agent Johnny Allen, whom she accused of rape.

Police said she shot Mr Allen in the back of the head at close range with a gun she brought to rob him after he picked her up at a drive-in restaurant in Nashville to have sex with her.

At the time of the incident, Ms Brown had run away from her adoptive family in Nashville in 2004 and began living in a hotel with a man known as "Cut Throat".

She alleged that he forced her into prostitution and verbally, physically and sexually assaulted her, according to court documents.

Her lawyers contended she was a victim of sex trafficking who not only feared for her life but also lacked the mental capacity to be culpable in the slaying because she was impaired by her mother's alcohol use while she was in the womb.

At the time of her conviction, the state of Tennessee argued successfully in lower courts that Ms Brown's sentence was not in violation of a federal prohibition on sentencing juveniles to life in prison.

The state argued then that she was not sentenced to life as she was eligible for parole after serving at least 51 years, which would have been in 2059.

In recent years, Ms Kardashian West has pressed US political leaders for prison reform. ( Reuters: Kevin Lamarque )

Book deal and documentary billed for Brown

Now 31, Brown will remain on parole for 10 years, on condition that she does not violate any state or federal laws, holds a job and participates in regular counselling sessions, Mr Haslam's commutation says.

Ms Brown released a statement saying she wants to help other women and girls suffering from sexual abuse and exploitation.

She also has a memoir coming out in mid-October and has gotten married, according to Yona Deshommes, associate director of publicity for Atria Books, her publisher.

In addition to her book, a documentary about her is set to be released this year.

"I thank [Mr] and [Ms] Haslam for their vote of confidence in me and with the Lord's help I will make them as well as the rest of my supporters proud," she wrote.

At the time of her sentencing, Ms Brown was not eligible for parole for at least 51 years. ( AP: Lucy Atkins )

Her attorneys said she's requesting privacy and transition time before she makes herself available to the public.

Mr Haslam said that was too harsh a condition for a crime Ms Brown admitted to committing as a teen, especially given the steps she has taken to rebuild her life.

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She earned her general equivalency diploma (GED) — a US and Canadian education certificate given to people who did not officially complete high school but completed alternative equivalent exams — and had also completed university studies as a prisoner.

Ms Brown met with prison counsellors to design a plan for her release, which will include time in a transition centre and continuing coursework with the Lipscomb University program.

Ms Brown, pictured in 2006 (left) and 2013, said she wants to help other women suffering from sexual abuse. ( Reuters/Tennessee Department of Corrections )

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