Actress Ruth Negga on the isolation of Iona

Edinburgh International Film Festival, and the hotel bar in the centre of the capital was buzzing. Movie people barked into mobiles, there were robust conversations about scripts and backing at nearby tables, yet in the middle of it all Ruth Negga sat quiet and still, legs curled up under her.

Petite, composed, dressed down in plain T-shirt and jeans, you might know her face as Raina in Marvel’s TV show Agents Of S.H.I.E.L.D or her voice as Shanalotte in the XBox Dark Souls II game, but she was here to talk about Iona. A more modestly-budgeted film, it was to have its world premiere that evening at the closing night gala and this week it goes on general release. Director Scott Graham’s follow-up to his award-winning debut feature, Shell, it’s as far away from the world of superheroes as you can get and Negga steals the screen, with an impressive support cast that includes Douglas Henshall, Tom Brooke, Michelle Duncan and young actors Ben Gallacher and Sorcha Groundsell.

Set on the tiny Hebridean island, the drama focuses on a young woman, also called Iona, who was raised in the Christian community and has returned with her teenage son, seeking refuge.“The location was important in the film,” says Negga. “It was so quiet and small, and the isolation helped. Iona went back to a place of safety and refuge, but doors kept closing and life just got harder and harder. I found that difficult because you form a love for your characters and want everything to be all right for them in the end.”

Ruth Negga and Joel Edgerton as Mildred and Richard in Loving, directed by Jeff Nichol

Like the island, the character of Iona is isolated and lonely, and the resulting film has a beautiful bleakness that doesn’t hold back. Negga admits it was a role she didn’t find easy to play and credits co-star Douglas Henshall for giving her the support necessary to go out on a limb.

“He is just so giving and sensitive. It was a very hard film to make emotionally,” she says. “I like to take control and being that vulnerable is hard; it affects you as a person. To be the target of so many tragedies, to have been abused so that there is a normalcy about it. That’s what would upset me most, that another human being can make you feel less than human, that someone else can break your spirit.”

She adds: “It was lonely playing Iona because she’s a lonely person – very different from me. I imagine she started off quite confident, happy, a bubbly person, and life just wasn’t fair. It isn’t fair.

“It made me think we have to look after each other because that’s all we have really, our connection to other people. That’s why Iona goes back to the island,” says Negga who relocated to London from her childhood home in Limerick, Ireland in 2006.

Unlike Iona, Negga has “a big Irish family” on one side, and “a big Ethiopian family” on the other. An only child, she was born in Addis Ababa, Ethiopia (“the only country that hasn’t been colonised,” she tells me proudly), in 1982, with an Irish mother and an Ethiopian father, and lived in the country until she was four when the family moved to Limerick.

“I never experienced racism but I definitely felt different. When you’re a different colour, and your father was, it has an effect on you. People are surprised when I say I’m Irish. There’s an expectancy that everyone has to have the same narrative. But I embraced it early on because the other option is to fit in. So there’s something about outsiders that I understand. Iona’s a misfit, and I don’t think she necessarily wants to fit in anyway.”

Negga’s father died in a car accident when she was seven, but she didn’t use her personal experience of trauma to identify with Iona.

“I’m familiar with loss. But I don’t think I drew on that specifically. It’s much better to provide a narrative for your character that is theirs. I don’t think people would last long doing this job if they did it that way.

“Anyway,” she says, and laughs. “I have a tragic face. I’ve done Lavinia in Titus Andronicus and Antigone. I have the face for Antigone,” she says, pulling a grief-stricken expression. Then banishes it with a smile.

Negga knew she wanted to act from a young age and, after studying acting at Trinity College, Dublin, was nominated as Most Promising Newcomer at the 2003 Olivier Awards. She made her screen debut in the 2004 Irish film Capital Letters, followed by the lead in Isolation. Director Neil Jordan changed the script to Breakfast On Pluto to include her and by 2006 she was Ireland’s Shooting Star for the Berlin Film Festival. On TV a performance as Dame Shirley Bassey won her the IFTA Award for Best Actress (Television) and since 2013 she has played Raina in Agents Of S.H.I.E.L.D. Films include Fury, alongside Samuel L Jackson and the Jimi Hendrix biopic Jimi: All Is By My Side. Then last year came her most high-profile role to date, the ass-kicking Tulip O’Hare in Seth Rogan’s AMC fantasy drama series Preacher.

Based on Garth Ennis and Steve Dillon’s cult 1990s comic, it features a conflicted Texas preacher, Jesse, who is on a journey to find God with help from his sidekick Tulip.

For Negga, Preacher is the best of both worlds, part fantasy, allowing her to draw on her childhood surrounded by her elder cousins’ Judge Dredd and Preacher comic books, and also rooted in a very real place.

“There’s something about comic books that gives you freedom. It’s like Greek plays, where things are also done in broad strokes, and they both have very important lessons in them, about hubris, morality, right and wrong.”

Strong and bolshy, Tulip is an unrepentant criminal and force of nature who loves fashion as much as fighting.

“Playing her was amazing,” says Negga. “She’s so much fun. I had to learn how to hold a gun properly, and do fight training. It was very freeing. She also has a lot of very colourful outfits!” she adds.

“But I’m sure not everyone’s happy about me playing her,” she says, suddenly changing tone and referring to the controversy over being cast as a character drawn as Caucasian in the comics.

“The original was white, blonde, and busty, with blue eyes. But things have to evolve,” she says.

Racial intolerance is also at the core of Loving, directed by Jeff Nichols, and due out later this year. Negga plays one half of an interracial couple in Virginia in 1958, who are sentenced to prison for getting married. It was during the filming of this that she had the trauma of her scenes in Steve McQueen’s Oscar-winning 12 Years A Slave being consigned to the cutting room floor.

“That was destroying,” she says with a sigh. “They rang me to tell me the sub-plot I was in had been cut. It was heartbreaking.” Then she brightens immediately: “But I was doing Loving at the same time, so it wasn’t so bad.”

Recently it’s been back to the world of fantasy adventure with Warcraft, adapted from the video games and novels, and directed by David Bowie’s son Duncan Jones. Think dying planets, invading orcs and doomhammer weapons. Negga can’t wait to see the finished version of this much-anticipated other-worldly offering, so different to the down to earth beauty and drama of Iona.

If she were able to avail herself of something from the world of fantasy or comic books, what would it be?

“An invisibility cloak,” she says, with the speed of someone who has definitely given it some thought. “Then you could just leave the house with no clothes and no make up.”

She can forget that, because tonight there’s a premiere to go to, and with our time up, clothes and make-up await. Ruth Negga uncurls her legs, jumps up, and weaves her way superhero fast through the busy hotel bar tables. She’s got an appointment with the red carpet to keep.

• Iona (15) is released on Friday