When the first season of the Channel 4 sitcom Derry Girls debuted in 2018, the show’s lead actor Saoirse-Monica Jackson had something of a flip out. Her performance as Erin Quinn, one of four Catholic schoolgirls (and an English fella) living in Derry on the Northern Ireland border in the final throes of the Troubles, was – she now realised – quite out there: full of adolescent facial contortions that dripped with awkwardness, disdain and indignation. Jackson had been inspired by the punk irascibility of her teenage cousin and the animated comic tics of Jim Carrey and Rowan Atkinson. But now she feared that she had blown her big break. “I felt in a perpetual state of fear,” recalls the 30-year-old Jackson now. “It’s crazy: I didn’t think of it as a risk when I was doing it because Lisa [McGee], the writer, instilled such faith in me. I’d basically auditioned and I just thought that Erin was very physical and that the madness of the world and all the characters around her would lend itself to a physical comedy performance.” Jackson, who was playing a teenager, but was actually 24, began to catastrophise. “When it first came out and it was commented on a lot, I felt extremely vulnerable and really anxious,” she goes on. “And felt scared that I would never get cast in anything else again. And I was terrified that I was just… bad.” It turns out that Jackson needn’t have worried. Over three seasons, Derry Girls became the most popular Channel 4 comedy since Father Ted, and broke viewing records in Northern Ireland. When it transferred to Netflix, the show became a global hit. And Jackson has, in fact, worked again, appearing this summer in the $190m DC superhero flick The Flash, alongside Ezra Miller and Ben Affleck. Upcoming, she is in the Paramount+ period thriller The Doll Factory, adapted from Elizabeth Macneal’s 2019 novel about scandal and murder in the Victorian art establishment in the buildup to the 1851 Great Exhibition. There’s also a Netflix series, The Decameron, based on Giovanni Boccaccio’s 14th-century collection of comic short stories. Still, Jackson finds that it gives her courage to remember the insecurity she felt in the early days on Derry Girls. “I was so absorbed in the anxiety of it that I forgot it was working,” she says. “It was obviously working. The show was a big success and people loved it. That was a lesson for me to learn creatively: if you half-arse a big decision, it’s never going to work and really land.” We are meeting at the end of the Observer’s photoshoot, at a studio in north London. It’s been a long day, but Jackson loves fashion and is down with all the dressing-up. Off-duty, she wears skinny jeans, Adidas shell-toes and a vibrant, brushed-wool Fendi sweater she bought in Rome while filming The Decameron. She’s much more poised than Erin Quinn, but shares her comedic timing. When a dog, belonging to one of the shoot team, becomes a little over-familiar with my trouser leg, Jackson scrunches her face and deadpans, “I feel cheated on now, because he was humping me and I thought I was special.” Derry Girls, the final season of which dropped in spring 2022, remains a touchstone for Jackson and probably always will. She grew up in and around Derry and went to an all-girls Catholic secondary school there, not a million miles from the one in the show. So it was not a surprise that the series resonated deeply with her; what was less expected was that the city has now become a tourist hotspot. “I don’t think anything will ever compare to that experience,” she says. “There will be other jobs where you move to a different country or they financially make you feel more secure or they will probably stretch me more emotionally as an actor. But the sentiment of Derry Girls and the fundamental change it’s made… Well, what can ever be as big as that personally for me? There will never be anything like that.” One moment where it clicked for Jackson came last year when Julian Smith MP, who was secretary of state for Northern Ireland under Boris Johnson, referenced the “brilliant” Derry Girls, which had just concluded, in a debate in the House of Commons. “That was one of the most surreal experiences I’ve ever had,” she says. “He gave this speech where he’s talking about the importance of the Good Friday Agreement and Erin’s monologue [in the final episode]. I did not think that a character I played in a comedy would be talked about in Westminster by one of Boris Johnson’s cronies. I just feel like I’m in an upside-down land! We made a show about girls talking about fingering and having a good time. And now this, it’s just so crazy.” Jackson leaves an extended, almost reverential pause, before adding solemnly, “Obviously Derry Girls is a lot more than fingering.” As Jackson notes, there wasn’t a great precedent of actors from Derry making it big when she was growing up. Bronagh Gallagher, who was in The Commitments and smokes a bong in Pulp Fiction, was the main one. Jackson’s dad, Sean, is from Derry, and her mother, Ruth, is from County Donegal, 20 miles away in the south, and she split her time between the two places. When she was born, Sean was an engineer and Ruth was a chef, but over the years they had “sooo many businesses”: her mother, for example, ran a pub and later became a child psychologist. Jackson, though, was always fixated on one goal, to act, and feels indebted to her parents for not trying to talk her out of it. “Especially now I’m older, I really appreciate the way I was brought up,” she says. “My parents had this belief in me that I didn’t really need to have a Plan B, because, if I had a Plan B, that means I didn’t really believe in Plan A. Which is fucking mental! For some reason, they just had this blind faith that it would be OK. But I had that blind faith, too.” After leaving home at 18, Jackson studied at the Arden School of Theatre in Manchester before moving to London. She did some odd jobs, such as hawking HelloFresh boxes door-to-door, while trying to find an agent. “My dad told me a story about him setting up a business when he was in his early 20s and he was ringing these companies to try and get them to buy whatever he was selling,” she says. “It was the point where I was looking for my first agent and he was like, ‘Remember, you only need one yes.’” Jackson’s intense bluey-green eyes go moist. “It’s making me a wee bit emotional thinking about it, but he said to me, ‘I would get up in the morning every day and I’d sit on the phone all day long and it could be nearly three weeks before someone said yes to me. But it only took one yes.’ And it was so applicable to what I was trying to do in acting: fake it till you make it.” In the aftermath of Derry Girls, Jackson has particularly sought out dramatic and non-comic roles. Landing Patty Spivot in The Flash, however, came totally out of nowhere. “It was this crazy whirlwind that I just couldn’t believe,” she says. “I never thought I’d be auditioning for a superhero film. So I just sent a tape and the director Andy [Muschietti], who’s a lovely little fella, loved it. He didn’t know that I was in Derry Girls or anything. It was just a random tape that he’d seen and he thought, ‘Why don’t we cast her?’ It all felt like a massive fluke.” From Derry Girls, Jackson had become used to TV’s long days, being in every scene. The Flash offered a change of pace and scale. “With these big jobs,” she says, “even when you’re a smaller part and you’re in and out, you’re still contracted for a big amount of time, which is like happy days!” The film shot on the Warner Bros complex in Leavesden, north London, and it was Jackson’s first experience of a studio film lot. “It’s more like a schoolyard outside the trailers,” she says. “It’s summer, it’s London, everybody’s hanging outside the trailers having a craic. And the lovely girl that played Supergirl [Sasha Calle], we got quite friendly, so we’d go over and knock on each other’s trailers after lunch going, ‘Do you want to go for a walk?’ It would honestly feel like a school trip sometimes.” Jackson often seems to form strong connections when she’s working. Jamie-Lee O’Donnell, Michelle from Derry Girls, is one of her best friends and they speak most days. On The Decameron, it was Zosia Mamet, who played Shoshanna on the HBO comedy Girls. In the series, Jackson plays Misia, a servant to Pampinea (Mamet), but mainly they bonded over their often mispronounced first names. (Famously, Ryan Gosling delivered a primer on how to pronounce Saoirse in 2015, when presenting another acting Saoirse, Ronan, with an award: “It’s Ser-sha, like inertia.”) “Exactly!” screams Jackson. “That actually was my first conversation with Zosia. We both have Scrabble-bag names: just like a hand in the bag and then a couple of vowels and a few letters thrown in and that’ll do you, those sort of names. We had different directors coming in throughout the series and they all gave us a combined name of Zersha or Zosha, which I loved. So we both answered to any pharmaceutical company that it sounded like after that.” The intense bonds that form on set are a big part of what Jackson loves about her job. “On The Decameron, we were basically each other’s family for seven months,” she says, “and acting is the most peculiar profession to speed up any intimacy. On day two, I had my fingers in Zosia’s mouth and she had her fingers in my mouth and… Haha, I’m sure that’s going to be so strange in print! But that’s what the job entails sometimes. And thank God you are a nice person after it, because otherwise it would be, ‘Oh, nightmare! They’ve been into my mouth and I don’t like them!’” I make the dad-joke insight that when Jackson talks about The Decameron, I can’t not picture David Cameron. “I rang my brother because I was elated about the job, it was a part that I really, really wanted,” she replies. “And he was like, ‘That’s really good,’ but he just naturally assumed I was going to be playing David Cameron’s wife. It’s a big leap but fair enough. A job I would happily do as well, if anyone’s reading this.” After playing a schoolgirl while in her 20s, Jackson was also particularly determined to land roles where she played her real age. “People are really nice to me and treat me with glass mittens on – that’s not the expression is it? – because they think I’m so young,” she says. “And sometimes people talk down to me because they don’t realise I’m a 30-year-old woman who’s been out on her own for years.” Jackson’s birthday was last month and she’s excited by kicking on with a new decade. “Your 30s always feel like the doing years, don’t they?” Jackson describes her life as more “chill” these days. She’s been seeing the Scottish DJ and music producer Denis Sulta (real name: Hector Barbour) for three years and they recently bought a place in Liverpool. “He’s from Glasgow and I’m from Derry, so geographically it’s bang in the middle. So it’s fair,” she says, smiling. “And I have a lot of family connections in Liverpool and childhood memories there. And it’s great for a blow-dry, all the beauty treatments are good, so it’s good for a Derry girl like me. Hec travels a lot and I do, too, but the times that we do get at home together are so lovely. The wee Liverpool hideout. The scouse house!” Downtime for Jackson is often spent cooking. She showcased some of these skills on the Great New Year’s Bake Off in 2020 when, as an unfancied outsider – she had never baked before – she destroyed four other Derry Girls cast members to walk off with the ornamental cake stand. “Oh Jesus, baking is a different beast, but my competition wasn’t high with the Derry Girls,” she says. “The standards were low, so that’s how I won that. My mum actually said she’s never been prouder and I was like, ‘Are you serious? I made a great cake and that’s what you’re proud of?’” We need to wrap up: Jackson has to get the train back to Liverpool. Derry Girls will always stay with her, but her career beyond the show is ratcheting up nicely. In 2021, Jackson met Joanna Lumley in Derry for the BBC travel series, Joanna Lumley’s Britain. Off-camera, the Absolutely Fabulous star asked Jackson how she felt about going up for different parts now and she admitted she was worried she might never escape from being associated with comedy. “And she gave me an amazing piece of advice,” says Jackson, picking up the story. “She was like, ‘You’ll always be a perpetual schoolgirl to some people in their eyes, but being in these comedy shows gives you a real ticket to the world.’ And I didn’t really know what she meant until a year or two later. But people are just so welcoming when they meet you sometimes. Not all the time, obviously. But when they meet me and they’ve watched the show and they associate you with laughter.” Jackson giggles, “They associate you with a joyous moment when they were laughing at you!” The Doll Factory is available to stream on Paramount+ now. The Decameron will be on Netflix in early 2024 Fashion editor Jo Jones; makeup by Amanda Grossman at The Only Agency using Dr Hauschka & Jones Road; hair by Ken O’Rourke C/O Management using Sam McKnight and Babyliss Pro; styling assistant Sam Deaman