Tyson, who hasn't had a bout in a year and a half, plans to fight seven times over three years to raise money to pay off debts of $38 million.
"I love to do what I do to pay all of my bills," Tyson said news conference in Louisville Tuesday. "I am the most foolish person I know. I am a fool, but I am glad to be back."
The former heavyweight champion turns 38 Wednesday. Williams is 30.
"I have a checkered past, but this is the greatest country in the world," Tyson said. "I certainly deserve a second chance to sweep the past away."
Tyson's record is 50-4 with 44 knockouts. Williams is 31-3 with 26 KOs. He is a former British Commonwealth heavyweight champion.