The rappers co-founded the organization with Patriots owner Robert Kraft, 76ers co-owner Michael Rubin, Brooklyn Nets co-owner Clara Wu Tsai and others. News commentator Van Jones was appointed CEO of the organization.
After Mill was sent to prison on a probation violation in November 2017, JAY-Z, Kraft, Rubin
The founding partners pledged $50 million to the effort, according to NBC News.
"Creating the Reform Alliance is one of the most important things I've ever done in my life," Mill said in a statement. "If you thought my case was unfair, there are millions of others dealing with worse situations and caught up in the system without committing crimes," he said. "With this alliance, we want to change outdated laws, give people hope, and reform a system that's stacked against us."
During a news conference Wednesday, JAY-Z applauded Mill for his activism and helping to bring light to the need for criminal justice reform for the nation.
"But for me, I'm from Marcy Projects. I'm from Brooklyn, and this has been a part of my life. This is communities we grew up in, friends that I have [and] people around me," JAY-Z said.
"We're all prisoners to this because until everyone's free, no one's free," he added.