In her teens, she auditioned for girl bands and cruise liners, dropping in and out of university to fund her ambitions with student loans.
Frustrated by failure, the Welsh-Greek chanteuse realised she needed to strike out on her own. So she taught herself piano and began writing spiky, memorable pop songs under the stage name Marina and the Diamonds.
Fearless, ambitious and stylish, her debut album The Family Jewels is a compelling pop confessional. Comparisons to Kate Bush and Siouxsie Sioux have been plentiful - but, on tracks like Shampain, she also channels the harmonic dazzle of Abba.
A series of low-key EPs built expectations among pop fans last year, but Diamandis says she feels no pressure to succeed.
"Not even one per cent, because the album is done and there's no going back. I've done everything I've wanted to."
Why did you choose Hollywood as your first single?
I'm saying: "This is who I was. Hollywood infected my brain and I really valued the wrong things in life, but I changed dramatically."
This obsession with celebrity culture is really unhealthy. I don't want to live my life like that, and I don't want to be a typical pop star.
Watch Marina and the Diamonds' video for her single Hollywood
What was the infection like? Did you run a fever?
Did I run a fever? I don't think so! I just liked the way it sounded.
Plus, I had this American boyfriend and I always got the feeling he thought everything should be like it is in the movies.
That poisons a lot of relationships, doesn't it? A lot of people feel every date has to be a "movie moment".
Yes, but not in a cynical way - that's just a young people thing. They think love is going to be one thing and it's something else.
There's never a comfortable silence in a Hollywood film...
Exactly! That's when you know you really fit with someone - when you can just sit there and not do anything. Kind of ignoring each other.
Was Hollywood the first song you wrote?
Actually, when I was seven, I made up an awful song up about a butterfly. It was so bad that I didn't try and write again until I was 17. Really shocking.
Once people hate me, I will feel fine with myself. Because that's my biggest fear - and when it happens I haven't really got anything to lose
What made you start writing again?
It wasn't hugely calculated. I just remember feeling, when I was going to these pop auditions, that I wasn't good enough to be in the pop game because my voice wasn't technically perfect.
And I remember thinking, I'm not a dolly. I've got something to add and you're not letting me do it. So I stopped auditioning and went out on my own.
How would your life have changed if you'd ended up in S Club 7?
I'd probably be a bit miserable. Just because... I don't think it's a bad thing but, for my personality, I really like having creative control and I don't think I'd have had that if I'd taken that route.
And you really hadn't had any musical training?
No way! I didn't even know what key my songs were in.
How did that lack of knowledge affect your songwriting?
Literally, on the most basic level, I did what sounded good. Just pressing buttons. And that's how I compose my songs still. I mean, I know the names of the chords now but I think I will actually learn as I go.
Judging by your lyrics and your blogs, you're often plagued by self-doubt. If you're really that fragile, is this a wise career choice?
I know it isn't - but it's like I have to do it to prove something to myself. I've absolutely been on autopilot for the last five years to get to this point. So I'm doing it, regardless of being in an industry that's very false and very fickle and sycophantic.
And once people hate me, I will feel fine with myself. Because that's my biggest fear - and when it happens I haven't really got anything to lose.
The 23-year-old was brought up in both Greece and Wales
Do you lie awake at night worrying about making the top 10?
God, no! I'd be ecstatic if I got in the top 40 because I've never even touched it. Being commercial isn't part of the plan. Nothing I do is pre-meditated. The point I want to put across is I would be doing this anyway.
Are you ready for the promotional treadmill of the music industry?
Actually, I think that a lot of the interviews and acoustic sessions and other things that artists fill their time with are really pointless and suck the energy out of the artist. So I've said to my label: "I will do two-thirds of it and the other third of my time I will spend songwriting." It's ridiculous that you would spend four months of your life writing and two years touring.
And then, every year, instead of doing the album format, I'll just do a six-track EP. So I'll have a constant flow of music and I'm never over-exposed because I don't spend all my time doing photo shoots and interviews.
I think it'll sustain my career as an artist as opposed to a pop star. I never really wanted to be a pop star.
Marina and the Diamonds was talking to BBC News entertainment reporter Mark Savage.
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