In 2017, he was handed a script called “Succession.” The part was for Roman Roy, youngest in the Roy clan led by media mogul Logan Roy (Brian Cox). Loosely based on the real-life Murdoch family of Fox News, the show quickly became a breakout hit, catapulting Culkin to center stage playing not a kid, not a ‘tween, but a man, albeit one with no spine. At first glance, he knew the writing was strong but didn’t see an audience for it, including himself.

“As we were shooting, I was like, ‘I might not watch it, this isn’t for me.’ And then something clicked,” Culkin tells The Envelope. “The first few episodes, they’re good, there’s quality there, but I just don’t care about the characters. And somehow after a few episodes, I started to care.”

If older brother Kendall (Jeremy Strong) is the Roy Family’s Fredo, Roman is Kendall’s Fredo. Overwhelmed with insecurity and a profound lack of impulse control, he is the show’s cringe king, initiating an affair with much older in-house legal advisor Gerri Kellman (J. Smith-Cameron), sending her crotch shots — accidentally sending one to his father.

Kieran Culkin often played the cringe king as Roman Roy in “Succession,” especially in his scenes with J. Smith-Cameron as Gerri.

(Peter Kramer / HBO)

As the series winds down, Roman, along with Kendall and sister Shiv (Sarah Snook), vies for control of the family company, Waystar Royco, even though in his heart he knows that he, like his siblings, is unfit to lead. The point is amplified by Logan, who tells them, “You aren’t serious people.”

“He could have raised them better, he could have taught them a bit better,” Culkin says of the fractious family dynamic. “In various ways, he taught them that emotions were weak, and they all handled them in very different ways. And I think that Roman was always just told to bury it. You can acknowledge that you love someone, just don’t show them love or give them love.”

Emotional impediments take center stage halfway through the fourth and final season when Logan dies unexpectedly. (No cries of “spoiler!” here, the show is called “Succession” after all). “Roman convinced himself that he had pre-grieved,” Culkin says. “He hasn’t been given a moment to actually accept what happened and how he feels and who he is. I don’t feel like he really knows himself, outside of being his father’s son.”

Although he worked steadily as a child actor, Culkin credits “Igby Goes Down” director Burr Steers for teaching him about process when he was just 20. “The next big one for me was doing ‘This Is Our Youth,’ with Kenny Lonergan,” he says of the 2014 Broadway production co-starring Michael Cera. “I had more of an understanding of language and how to play with it. On stage, you’re not playing with the dialogue. Without changing a single syllable there’s room to play.”

Up until “Succession,” Culkin would prepare by getting off book and absorbing the full arc of his character. But with the hit series, they got scripts and changes so late that he was seldom sure of his lines. “The nature of the writing was very alive but very last-minute. So, I had to completely change my process,” he notes.

Much has been made of Strong’s Method acting, but Culkin found himself adjusting to all of his co-stars, including Matthew Macfadyen and Nicholas Braun. “Brian worked differently than anyone else. If we did a group scene, we knew the lines but were encouraged to talk over each other and try it a different way, or stay loose with blocking. That would throw Brian. So, we’d often have to stay pretty tight to the script. Then, if I have a scene where it’s just me and Sarah or me, Sarah, Matthew and Nick, we can play a lot more. With Jeremy, there were times to play, too. It wasn’t like we had to stick to a certain way, but we did have to adjust to personal preference. And now I have to go into my next job knowing that they’re probably not going to let me do what I did on ‘Succession.’”

Kieran Culkin stars with Jesse Eisenberg in the Sundance hit “A Real Pain.”

(Sundance Institute)

The next job was “A Real Pain,” starring and directed by Jesse Eisenberg, which recently premiered at Sundance to stellar reviews. In it, Culkin and Eisenberg play cousins who travel to Poland to honor their grandmother, a Holocaust survivor, following her death. Early press had noted on-set differences between Culkin and Eisenberg.

“He had a very set way that he wanted to direct this film, and I was like, ‘I don’t even get to pick my own blocking.’ That feels weird. It’s his film, not mine. I don’t want to step on his toes. But if I’m hired to do a job, I feel like, to a reasonable degree, I should be able to do it how I want. So, I think for a day or two he was a little bit sensitive about this process. And after a few days, we started to adapt a little.”

His recent though long-delayed Emmy for lead actor in a drama series (besting co-stars Strong and Cox) joins his Golden Globe and Critics Choice Awards, well-deserved accolades, though some question whether Roman is a lead role.

“I wanted to switch categories [to lead], and I got a lot of pushback on that,” Culkin says, noting HBO was supportive but others told him he’d be hurting his odds that way. “If switching to the other category meant accepting that I would not be receiving any awards, I was fine with that. Snook and I said that we should switch two seasons earlier. She and I switched this year.”

During his acceptance speech, Culkin gave a shout-out to his wife, holding her to a promise that if he won, they would start planning for more children. Toward the end of our interview, he receives a photo of his kids playing in the snow in Central Park and is reminded of his own childhood with his six brothers and sisters, raised in a single room in Manhattan’s Yorktown neighborhood by their mom (whom he thanked in his acceptance speech). “I really wish I was there for it,” he says, looking at the photo. “Those moments really matter.”