Jay and Meek have helped launch a criminal justice reform organisation aimed at reducing the number of people in American jails.
Reform Alliance is putting $50m (£38m) toward “disabling the revolving door of probation and parole”.
Speaking at the launch, Jay said: “We want to be very clear – if someone commits a crime they should go to jail but these things are just disproportionate and the whole world knows it.”
According to civil rights group, the NAACP, black Americans are jailed at a rate of five to one in comparison with white American offenders.
Mill – who real name is Robert Williams – was recently released from prison for parole violation stemming from drug and possession charges in 2008. His conviction sparked a national conversation, with many high profile celebs calling for his release.
“I’m here to speak for all the people who don’t have a voice,” he said.
“Being from the environment I’m from, I don’t even think it’s possible for you to be an angel.
“You grow up around murder on a daily basis, you grow up in drug-infested neighbourhoods on a daily basis.
“I got caught up in the system.”
The Alliance’s goal is to free one million people from the system in the next five years, focusing on on parole and probation.
America still has the distinction of having the highest incarceration rate in the world.