‘I’m enjoying the fuck out of my job!” Kieran Culkin announces, with the same foul-mouthed ebullience one might expect from his character in Succession, the compulsive drama about a vicious media dynasty. It becomes easy to imagine that it’s his small-screen persona sitting in front of you in a conference room in HBO’s New York office, only without the fancy jewellery and stinging bile.

New York? “It’s fucking impossible to live here!” Ratings? “I don’t give a fuck!” Erm, Only Fools and Horses? “I fucking love that show!”

The 36-year-old former child actor is in high spirits. It’s the morning after the first show of the second series: the reviews are good and so is the social media response, with myriad lustful tweets aimed Culkin’s way. (“You should get my wife to see that,” he blushes.) He’s five minutes late and – unusually for an actor – apologetic about it. On arrival, he asks a publicist for a Coke and proceeds to explain his problems with aspartame, detail how vacuous parts of Los Angeles can be, and then tell an anecdote about frustratingly unnamed celebrities behaving badly in the Chateau Marmont hotel. Even when talking about things he dislikes, there’s something likable about the way he frames it, a devilish smile emerging throughout.

Cutthroat world … Kieran Culkin as Roman Roy in season one of HBO’s series Succession. Photograph: HBO/Peter Kramer/Bravo

It’s a similar quality that makes his performance in the Emmy-nominated drama so magnetic. As Roman Roy, the brattish, brutish son of a Rupert Murdoch-esque media magnate, he plots and curses his way through the cut-throat world of Succession. Crafted by Peep Show co-creator Jesse Armstrong, the blackly comic drama has become one of TV’s most addictive pleasures. It’s unapologetically, aggressively nasty. I tell Culkin I was initially turned off by the concept of watching an obnoxious, rich family get richer and even more obnoxious.

“I had that exact feeling when we shot it,” he says. “When we read the pilot, I thought this is very well written, I love this character, I would love to play it but I don’t know who would want to watch.” It took him five episodes to realise that not only would people care – they’d become obsessed. “There’s something that draws you to these characters even though you don’t give a fuck about them.”

His character was a fan favourite in season one thanks to his seemingly unending stream of vulgarities: in episode three he masturbates victoriously against the window of his corner office, thinking about the proles on the street below. Nonetheless, as the show progresses, Culkin is worried about the dangers of self-parody. “Here’s a sentence that I dread will come out on set: ‘That’s so Roman,’” he says, eyes rolling. “There are directors who will come in and see it like, ‘This can be like an iconic character if he’s treated this way.’ It’s like no, he’s actually just a person.”

While he’s gratified by the reviews and his Golden Globe nomination last year, he’s mainly relieved not to be mistaken as much for another Culkin. “I get [called] Rory and Rory gets called me,” he says of his actor brother, six years his junior. “A lot of the crew come up and say they worked with me on Mean Creek” – the 2004 coming-of-age drama that starred his brother. “I’m like, ‘Oh you did? Was I cool?’”

His family name has long preceded his first, thanks to the success of his older brother Macaulay, who became the world’s most famous kid in 1990 with the release of Home Alone. Kieran first appeared alongside his brother as bed-wetting Fuller in the Christmas comedy before taking roles in Jean-Claude Van Damme’s action film Nowhere to Run and two Father of the Bride movies. But despite having been prolific – he’d made seven movies before he turned 13 – he rejects the obvious label. “I managed to avoid being a child star,” he tells me. “I just did the thing and I was a kid. I went home, played video games.”

Kieran Culkin (left, front) in 1990 with his brother Macaulay Culkin, father Kit and mother Patricia. Photograph: News UK Ltd/REX/Shutterstock

The experience, he says, was boringly normal. Enrolled at a school that catered for children who worked, Culkin studied alongside musicians, dancers and golfers. He credits school with helping to avoid some of the excesses that have afflicted many child actors. “If you’re surrounded by other people in that situation, you compare yourself to others and just know that that person has their head up their ass,” he says. “I didn’t have an image of myself as an actor when I was a kid, if that makes sense.”

His childhood wasn’t without its setbacks. His father, Kit, was an unsuccessful actor who brought up his eight children to be performers whether they liked it or not, all of them living in a boxy railway apartment in New York. In the 90s, Kieran was caught in the middle of a custody battle won by his mother, Patricia, and remains estranged from his father. The press at the time was difficult to endure. “Sometimes they just fully fabricated stories,” Culkin says. “They would get lots of details way wrong – our names, our ages, things like that. So I grew up going OK, not everything that you read is true.”

Tabloid attention was intensified by the fact that Macaulay was a close friend of Michael Jackson, regularly visiting the singer’s Neverland ranch with Kieran in tow. “I have slept in a bed with many children,” Jackson told Martin Bashir in 2003. “I slept in a bed with all of them when Macaulay Culkin was little. Kieran Culkin would sleep on this side, Macaulay Culkin was on this side. We all would just jam in the bed.”

It was a creepy enough anecdote at the time, but since HBO’s devastating documentary Leaving Neverland, in which two victims said that Jackson had subjected them to years of sexual abuse, it seems particularly grim. Culkin shifts uncomfortably, but he has seen the question coming – he tells me that he realised I would ask him about Jackson before the interview. He points out that he doesn’t have media training, signalling that what follows hasn’t been publicist-approved.

“The only thing I can say is that I can’t really say anything and the reason for that is I can’t be helpful to anyone,” he says earnestly. “To me, it seems like there’s two sides to this thing and because I can’t be helpful on one side or the other, anything I say and anything that gets put out in print could only hurt somebody and there’s already a lot of really hurt feelings. There are already a lot of people who are in a difficult position and if I contribute in any way, it’s just going to hurt someone because I can’t actually help.”

He won’t be drawn any further, so I ask him about the recently announced plan to reboot Home Alone, news that takes him by surprise. “That kid would definitely be fucked up by now,” he says, adding that the original film “still holds up. It still makes me laugh and I can’t wait to show my kids.” Culkin’s wife, British former model Jazz Charton, is eight months pregnant, something that makes him “excited”. Would he encourage his child to follow his career path? “If the kid wanted to get into acting, I’d be all for it,” he says. “Not a lot of former child actors would want to put their kids through it.”

It took until I was 35 and I had been doing it for about 29 years for me to go, ‘Hey, I think I want to be an actor'

Culkin says he suffered a crisis of confidence at 20. After his acclaimed turn as a spoilt slacker in 2002’s Igby Goes Down, “I realised I’d been doing it for 14 years and I never once made the decision ‘Hey, I want to be an actor.’ So I flipped out and – you can check my IMDb – I didn’t work for years. I didn’t know what I wanted to do with my life.”

It was only with Succession that he became comfortable with acting again. “We were shooting last season when I came home one day and I said: ‘I think this is what I want to do.’ It took until I was 35 and I had been doing it for about 29 years for me to go, ‘Hey, I think I want to be an actor.’” Besides, he adds, “baby needs food”.

Despite this newfound passion for who he is on screen, he’s still unsure about how he presents himself off it. “I’m terrible in print because I just sort of speak in these fragments and then it’s your job to try to piece it together and make some sense,” he says. Does he enjoy doing interviews? “I have a feeling you’re saying this because I’ve already fucked myself two or three times?” he laughs quizzically. But as Roman would put it, hell no – only with a stronger expletive.

• Season two of Succession is on Mondays on Sky Atlantic and Now TV.