Not so long ago, Samantha Morton was given a relic from her past – her application form to join Nottingham’s Central Junior Television Workshop (one of the organisation’s leaders, clearly proud of Morton’s success, had hung on to it). It had asked her to list what she wanted to be when she grew up. Prime minister, she wrote, followed by novelist and actor. She laughs, remembering it. We had been talking about whether she might go into politics one day – not such a leap for an actor who is intensely political (the “novelist” bit might have to wait). But it also seems to sum up so much else about the young Sam I’m picturing, defiant blue eyes staring out from the scrappy passport photo that would have been stapled to the corner of the sheet. Drive and ambition, and a feeling that despite everything she had been through by that point – in and out of care for years, subjected to physical and sexual abuse – that her hopes and dreams could be as big as anyone’s.

Through immense talent, luck and sheer force of will, Morton, 45, did make it – Hollywood success, indie superstardom, two Oscar nominations, a Bafta for the first film she directed, and now starring roles in big TV shows. She was in The Walking Dead, playing Alpha, the leader of a zombie army, and has just been announced as the lead in another series, The Burning Girls. Her latest is in The Serpent Queen, as Catherine de Medici, the 16th-century queen of France, vilified throughout history, but portrayed here by Morton with characteristic empathy (and based on the biography by Leonie Frieda).

How did she get into the head of such a legend? “I think ultimately with any character, it’s about finding them in a private moment,” says Morton, speaking over Zoom from a home that looks lovely, with old wooden beams and plenty of art. “When I’m alone with the scripts, I need to be able to see in my head who they are, how they walk, how they breathe.” Morton didn’t know much about Catherine, but realised she “had permeated my life in all different ways, from Disney films to Grimm fairytales to the arts. She was an original thinker. She was massively educated, spoke many languages, was a great mathematician, astrologer, astronomer.”

She is always, says Morton, “the smartest person in the room, and then has to almost dumb down in order to facilitate other people’s egos and make sure that …” She pauses. “Make sure she’s going to survive. She can’t expose herself as being intelligent. Intelligent women are dangerous, no? She was able to overcome all those obstacles and not only survive, but she thrived and she became the longest ruler in France. It’s an extraordinary story, knowing – as much as we can tell, because history is written by men – that it was true.”

Some of the themes, she adds, are as relevant today as they were then, “certainly the ownership of a female body, and how they talk about young Catherine getting pregnant [her worth was in providing heirs, and she didn’t conceive for 10 years]. We only have to look at what’s happening in America, and what’s potentially going to happen in the UK, in regards to the ownership of our bodies by the state. Any woman watching the show will have something in common with her, because of the way times are changing for us.”

Then there are personal similarities between Morton and Catherine – the resilience, the survival instinct – if at opposite ends of the privilege scale. Morton was first taken into care as a baby, and later was made a ward of court – under the responsibility of the state, like Catherine, an orphan who grew up in a convent until her marriage to the second son of the French king Francis I. “She was given the best education money could buy. I’ve often said, when I was in care, it would have been great if I’d have been sent to a fancy boarding school because at least I would have come out of it …” She pauses again. “I might have been scarred in some way, but I would have had a great education at the end of it.” Many children in care, she points out, leave “with no GCSEs and no future that doesn’t just tick the statistic box of ending up sadly in prison or homeless”.

Where Catherine is calculating and cunning, Morton seems instinctive. Would the actor have had a different type of career if she had played the game? “Oh, yes,” she says instantly and laughs. “But how long wouldthat career have lasted?” When she was still building her career, she called out sexist comments, and did things such as tell executives to “fuck off” – she was to star in one big Hollywood movie, but was appalled when she was asked to wear a skirt to dinner with executives, and relayed the message through her agent. “I didn’t play the game and those actresses that did, and knew how to, are certainly very successful today. I just had to be able to go to bed at night and be comfortable with myself.”

She preferred, she says, “staying in the independent film sector whereby I had really good relationships with directors and producers. That worked for me because a lot of the people that were in power back then were people that I didn’t feel very safe around.” She has spoken before about being touched inappropriately and repeatedly on film sets. Long before the film producer Harvey Weinstein was exposed as a sexual predator, she was one of the few young actors who had publicly denounced his bullying behaviour; she was dropped from the film The Brothers Grimm after Weinstein allegedly said male stars would not want to have sex with her. One of Morton’s upcoming roles, with delicious irony, is in She Said, about the New York Times journalists who broke the Weinstein story; she plays Zelda Perkins, the former Miramax assistant who reported Weinstein to her bosses in the 90s and was forced to sign a nondisclosure agreement.

Anyway, says Morton, the choices she made worked out. “I’m still working.” Does she feel vindicated? She is a hugely respected actor, with an impressive body of work behind her, and now she’s doing the big, well-paid TV jobs, too. “I don’t know if I feel vindicated,” she says. “I feel sad that we got to where we got to, and I feel devastated for people that were abused. I sometimes look back, doing the kind of films I was doing or auditions and how I was treated, and just go: ‘That just wouldn’t happen today.’ It shouldn’t have happened then.” What sort of things? “Just that women were treated a certain way in the 90s and 2000s, we just were in any industry – there was misogyny everywhere. And there still is – I think there’s misogyny on film sets still, and we have to deal with it on a day-to-day basis. That can even be down to how people talk down to us, or how they talk to the makeup team or female runners. It’s a pretty male industry.”

She was ambitious to make good work, not necessarily good money, which made her more selective. “I was from a situation where I had no money at all, so any money was a bonus, and I knew how to budget and look after myself. If I wasn’t working for seven or eight months because I didn’t want to do the projects that were available, I’d be like, I’ll go and try my hand at poetry. I’ll go and retrain, go to college.”

Morton grew up in Nottingham. She has always spoken with love about her parents, who had nine children between them, but it was not a safe environment in which to grow up; her mother, having endured her own traumatic childhood, had poor mental health and Morton has said her father could be violent. After she was taken into care, she would return on and off to her father, who had custody, before permanently moving into the care system, which meant going in and out of foster homes and then children’s homes. In 2014, she spoke about being the victim of sexual abuse at one home – she reported the abuse to her mother and the police and she was moved. No action was taken against the perpetrators. At the next home she lived in, she experienced physical abuse. She would run away, sleeping rough rather than stay at the home, and shoplift food.

At 13, she left school, but around this time she also got a place at what was then the Central Junior Television Workshop. Within a couple of years, Morton was getting acting roles in London – in TV shows such as Cracker and Band of Gold, and in theatre. She had grit in abundance, but it gave her discipline and made her realise a successful career would involve sacrifice and commitment. One of her best friends was killed in a car accident and the funeral was scheduled for the first day of rehearsals at the Royal Court theatre. “The director said: ‘If you don’t turn up, you’re not in the play,’” says Morton. “I remember thinking how tough that was, and talking to my friend’s mum and her saying: ‘She’d want this opportunity for you.’ I was living in a homeless hostel at that point.”

Even if she didn’t entirely play the Hollywood game, Morton’s career rocketed – roles in Woody Allen’s Sweet and Lowdown, which brought her first Oscar nomination (the second was for the immigrant drama In America), and Steven Spielberg’s Minority Report, as well as British independent films such as Morvern Callar. Many of her roles, including as an 18th-century brothel owner in Harlots or as a single mother forced to sell sex to survive in I Am Kirsty, have portrayed women who are judged by society. “Certainly, a lot of the roles I’ve chosen have had a social …” She thinks of the word. “An edge to them.”

Morton’s 2009 film, The Unloved, about a young girl going into care, did incredibly well – 3 million people watched it on TV, and it won a Bafta and a best actor award for Robert Carlyle – but frustratingly, Morton has found it hard to get funding for her next film, Starlings, intended to be the second of a trilogy. “Film4 didn’t want to make the film with me, which broke my heart a little bit because they’d made The Unloved. They didn’t even want to read my script,” she says. “The BBC didn’t want to read my script either. I don’t know that if I was Michael Winterbottom they might want to, but I found all that really tough.” Is it harder for female film-makers? “One hundred per cent. I think a lot of the people that make the decisions about films are men, and for some reason, they trust male film-makers – even if they’ve only done a commercial or a music video, they seem to trust them [more].”

At one point, Morton says: “I think the older I get, the more little Sam is almost something in the distance,” but if her own trauma is lessened, the issues that affected her as a child – and that children are going through today – are still things she thinks about on a daily basis. She has been “ranting and raving”, she says, about the effects of austerity for years, and with the cost of living crisis, life is going to get a lot worse for the most vulnerable in society. “It’s always the children that suffer the most when there’s poverty, depression, alcoholism, addiction problems. When people have it really tough, children suffer the most.”

Child protection services are grossly underresourced and in need of reform, she points out. “This isn’t rocket science – this can be fixed with the right attitude, and knowing how to spend public money, but it seems those things are shoved under the carpet by successive governments.” Every so often, when a horrific story breaks about child abuse, she says, “the whole country will go: ‘Aren’t those people evil?’” She would rather people ask, she says: “What could we have done as a society to have helped that situation have a different outcome?” It is frustrating, she says, because some of the answers are “not out of the reach of any politician. They’re things that can happen. They need money, they need the right people, but we’re not asking for the world.” Meanwhile, the top 10 providers of children’s homes made £300m profit last year. “Why would you privatise the care of young people? If you privatise everything, we’re in a really bad situation.”

There is something so bracingly uncompromising about Morton, and she has an eye on the wider issues – it has never just been about her. In some ways, this helped – she instinctively understood from a young age that none of what she went through was her fault. “I was almost caught up in someone else’s tornado,” she says. “I was kind of collateral damage.” But I still don’t know how she survived (personally, she seems incredibly happy, and is married with three children). She has had “lots and lots” of counselling, she says; the drugs she took as a teenager, particularly psychedelic drugs (now being researched as treatments for depression), may have had a therapeutic effect, she thinks. “I’ve dabbled and experimented with all sorts of ways to heal trauma, because there must be trauma.”

Faith helped – a mix of the Catholicism of her childhood, and other spiritual elements she has picked up. She feels loved, she says. “I have a huge amount of love for people and the world. I never felt hate.” Mostly she feels very lucky. “I count my blessings each day. My family might think I’m a bit weird, but I always go: ‘Let’s just have a moment. How lucky are we right now?’” She smiles, face lighting up. “It can get a bit annoying.”

• The Serpent Queen starts 11 September on Starz Play, and streams on Stan in Australia. She Said is out in November.