A social media campaign using the hashtag #FreeCyntoiaBrown went viral thanks to the stars' support

A US trafficking victim serving a life sentence for killing a man who paid her for sex when she was a teenager was released on parole Wednesday, following a celebrity-backed viral campaign for her freedom.

Tennessee Governor Bill Haslam commuted Cyntoia Brown's sentence in January, saying she had been given "too harsh" a punishment for the 2004 murder of a real estate agent in the city of Nashville.

Brown, now 31, was released from prison early Wednesday morning, according to the Tennessee Department of Corrections.

Conditions of her parole include that she comply with an approved release plan, remain employed or educationally enrolled while on parole, and attend regular counseling sessions.

She must also complete at least 50 hours of community service over the course of her 10-year parole period, US media reported.

Johnny Allen had picked up Brown, who was 16 at the time and a runaway under the influence of a dangerous pimp, and taken her to his home for sex.

The ex-Army sharpshooter allegedly showed off his firearms and "grabbed" Brown forcefully between her legs. She said she shot him in fear for her life.

Brown was tried as an adult and convicted of first-degree murder and aggravated robbery. She was given life with the possibility of parole after serving at least 51 years in prison.

Brown's case was featured in a 2011 documentary and attracted the attention of several high-profile celebrities, including singer Rihanna and reality star Kim Kardashian West.

A social media campaign using the hashtag #FreeCyntoiaBrown went viral thanks to the stars' support, and an online petition delivered to Haslam amassed more than 325,000 signatures.

Without Haslam's intervention, Brown would have remained in prison until at least 2055.

In a statement released after she was granted clemency, Brown thanked her supporters and the governor and promised to "do everything I can to justify your faith in me."

"My hope is to help other young girls avoid ending up where I have been," she added.