Dunigan, a founding member of the group, died in his sleep Friday night at his mother's home, DJ Paul told The Hollywood Reporter.
"He said he was tired, he wanted to sleep," Paul said. "He sat down at the kitchen table, put his head in his arms to lay down ... to get some sleep."
Paul said Dunigan's mother was not home at the time and discovered her son dead at the table when she returned.
Three 6 Mafia had recorded since the 1990s. They recently released their reunion album 6ix Commandments and were planning a show in the Memphis area next week.
"This year was going to make our twenty-fourth year rapping together," said Paul. "His music, our music that we made together, was truly before its time."