The two Detroit rappers first met in their home town in 1997 at a concert and worked together under the name Bad Meets Evil.
One of the songs they recorded in the 1990s, called "Bad Meets Evil," appeared on Eminem's major label debut, "The Slim Shady LP."
According to a news release from Interscope Records, the two pursued solo careers after their initial work together and became embroiled in a feud.
In the years since, Eminem's career has reached superstar levels with tens of millions of records sold and Grammy and Academy Award wins. Royce da 5'9" also has seen success, but on a much smaller scale, with three of his albums charting in the R&B/hip-hop category.
The two mended fences, however, following the shooting death of their mutual friend and fellow rapper Proof in 2006.
"Royce and I started hanging out again and inevitably that led us back into the studio," Eminem said in a statement. "At first we were just seeing where it went without any real goal in mind, but the songs started to come together crazy, so here we are."
The new material will be released June 14 on Shady/Interscope Records.
The Associated Press contributed to this report.