“Sing Sing,” arriving in theaters Friday with Colman Domingo, is a valentine to the valuable work at the Ossining, New York, maximum security prison since its Rehabilitation Through the Arts (RTA) theater program for inmates was begun decades ago.

The film not only has an Oscar-nominated actor as its lead but many actual inmates playing themselves.

“They invited me to collaborate with them — because they didn’t have a script at first. They basically had an article from Esquire magazine,” Domingo, 54, said in a Zoom interview. “I read about this RTA program at Sing Sing that was pretty fascinating. Then they told me they really wanted to tell their story in some way.

“I just really helped bring it to fruition by being very much in the center of it.”

Domingo plays a real inmate, John “Divine G” Whitfield, the troupe’s unofficial director who wrote the plays they performed, acted and mentored.  Whitfield was sentenced 25 years to life for a murder he didn’t commit – and spent his time as a jailhouse lawyer helping inmates gain parole.

“Sing Sing” is the first time Domingo has worked with non-professional actors.

“That wasn’t daunting at all. It was actually a great, beautiful challenge. Because I know they’ve been trained. They’ve been trained from anywhere, whether it’s Julliard or by being a working artist. Which is how I got my training.

“What was interesting is that these gentlemen will be able to bring their life experience as well to the work — and that’s something I could learn from.

“Whatever they didn’t know from creating film, I could teach them. So, it became this beautiful hybrid of working and I think we created something strong and beautiful because of it. Because everyone leaned into each other.”

In the last year, with his Oscar-nominated “Rustin” performance contrasted with his abusive husband in “The Color Purple,” Domingo suddenly broke out to become a star. Did he feel this would happen?

“To be honest, I always wanted to be a working, respected actor — and that’s what I’ve been for 34 years. I did not know that this chapter would happen to me. But I think I can see it because there’s been building blocks for many years of things that I’ve been doing — on Broadway, Off Broadway, being a writer, being a director, being a producer. I can see the path to this stage where we’re meeting right now.

“I feel like it’s outside of my brain. But I’m glad that I’m here, that I know myself and I’m as grounded as when I started out.”

“Sing Sing” opens in theaters Friday