President Trump has granted clemency to 63-year-old great grandmother Alice Johnson, who has been serving life in prison for a non-violent drug offence.
The case was highlighted last week when Kim Kardashian West met Mr Trump to lobby for her release.
The White House said she had been a model prisoner and worked hard to rehabilitate herself.
Johnson was jailed in 1996, with 15 others, for taking part in a cocaine distribution ring.
She was convicted on charges of attempted possession of drugs and money-laundering in Tennessee and is expected to be released soon.
Long battle finally over
Analysis by Jessica Lussenhop, BBC News, Washington
After four years and two presidential administrations, Alice Marie Johnson is finally going home.
I first began communicating with Ms Johnson as she waited to hear whether or not she’d been approved under President Barack Obama’s Clemency Initiative in 2014. She easily met all of the criteria, she had a spotless disciplinary record and even her own warden felt that she deserved to go home.
But days before he left office, Mr Obama denied her as well as hundreds of others. She swore to me she would never put her family through this process again – the disappointment was too painful for her two daughters.
Renewed hope came in the unlikely form of a reality TV superstar – Kim Kardashian West, whom Johnson began referring to as her “war angel”. Today, the long battle is finally over, though it is more a testament to the arbitrariness of the clemency process than anything else.
According to Ms Johnson’s lawyer Brittany K Barnett, it was Kardashian West herself who called to deliver the news to Ms Johnson.
“Overwhelmed with emotion, Alice said it feels like she has been ‘resurrected from the dead and she has her life back’.”
What did the White House say?
“Ms Johnson has accepted responsibility for her past behaviour and has been a model prisoner over the past two decades,” the White House said in a statement.
“Despite receiving a life sentence, Alice worked hard to rehabilitate herself in prison, and act as a mentor to her fellow inmates.”
The statement added that the administration believed in being tough on crime but believed in giving a second chance to those who tried to better themselves in prison.
How did Kim Kardashian get involved?
Kardashian West joined what has been a long-running campaign for Johnson’s freedom, spearheaded by the clemency foundation CAN-DO, friends and family.
She was first alerted to the issue after spotting a video about the case on social media.
Kardashian West visited the White House with her lawyer, Shawn Holley, and had also linked up with Mr Trump’s son-in-law and presidential adviser, Jared Kushner, who has been lobbying for prison reform.
In a tweet shortly after the White House announcement, Kardashian West described Alice Johnson’s clemency as inspirational.