In a public service announcement (PSA) posted to YouTube, the hip hop star, real name Terrence LeVarr Thornton, read out the words of Norman Brown, who was jailed for life without parole when he was 22.

He was in prison for 15 years until 2010 when U.S. President Barack Obama commuted his sentence.

Brown's sentence was handed down after he was found guilty of six counts of crack cocaine distribution, and he received life without parole under America's mandatory minimum sentencing laws as he had prior convictions.

Reading Brown's words in the PSA, Pusha said, "When I was found guilty I had to ask myself, 'was I ever going home again?'"

The rapper related how Brown had gone off the rails at the time of his arrest but in prison had studied to take his mind off the harsh prison conditions and helped other inmates learn job skills.

Explaining how Brown had lost faith he would ever leave prison, Pusha continued, "In 2010, I filed for clemency, but I'd lost hope in the system. I'd been in for 15 years and several motions had been denied. While in prison, my mother, my father, my brother and my grandmother all died. My daughter was also born. In many ways, we grew up together."

Earlier this year (16), Pusha was among a group of artists who met with President Obama to help create support programmes to help young men of colour fight racial injustice.

Over the course of his eight year presidency Obama has commuted the sentences of a record 1,176 prisoners and pardoned 148 people, and has particularly focused on those jailed under mandatory minimum sentencing.