Albert Woodfox was convicted twice for killing a prison guard in 1972 but a judge ordered his release last summer.
The former Black Panther was kept behind bars by a federal appeals court as the state of Louisiana, where he was imprisoned, lodged a challenge against his release.
His release on Friday came after the state dropped the threat of a third murder charge in exchange for Woodfox pleading no contest to lesser charges.
‘Cruel and inhumane’
“Although I was looking forward to proving my innocence at a new trial, concerns about my health and my age have caused me to resolve this case now and obtain my release,” Woodfox said in a statement after he was freed.
Woodfox’s supporters have insisted his imprisonment and detention in solitary confinement were politically motivated.
His legal team has called on authorities to end the use of solitary confinement as a punishment, describing the practice as “cruel and inhumane”.
The activist was one of three men known as the “Angola Three”, alongside Robert King and Herman Wallace, who supporters say were kept in isolation because they fought for better prison conditions.
King was released in 2001 after his conviction was overturned and Wallace died in 2013 just two days after his release.
The Angola Three of the Black Panther Party were kept in solitary confinement for decades. [AP (Archive)]
Meanwhile, Barack Obama used his executive powers to ban solitary confinement for juveniles in all federal prisons. He has also commissioned a review into the use of solitary confinement in the US.
“If our ultimate goal of our criminal justice system is to give people a second chance, after they’ve paid their debt to society, we’re basically setting them up to fail if we don’t take seriously the long-term negative consequences of prolonged solitary confinement,” President Barack Obama’s spokesman Josh Earnest told reporters.
“The kind of reforms that the president put forward are the kind of reforms that can only be implemented in the federal prison system,” he said.
His two fellow Angola Three allies were already freed. Robert King, who spent 29 years in solitary was released after having his separate conviction overturned, Herman Wallace was released in 2013 and died shortly after of cancer.
Yet many of the 80,000 people estimated to be in solitary confinement in US prisons have been there for years on end.
“Today should also mark a pivotal new chapter in reforming the use of prolonged solitary confinement in US prisons and jails,” said Jasmine Heiss, a campaigner with Amnesty International USA.
“Moving forward, Woodfox’s case must serve as a tragic reminder of the cruelty inflicted by the prison system at its most extreme.”