Douglas will play the famed glamorous musician, and Damon his significantly younger lover, Scott Thorson.
"I don't think I would have had the courage at that point in my career to take this on," Douglas said in praise of Damon.
The two lead actors and Soderbergh said they took the story seriously despite the over-the-top nature of the subject matter, The Hollywood Reporter said Friday.
"We take the relationship seriously," Soderbergh said.
"We weren't giggling about it. These were people's lives. We wanted to get it right," Damon said.