The 31-year-old from London confessed to feeling nervous before her big performance in front of the judges.
As Amanda Holden, Alesha Dixon, David Walliams and Simon Cowell waited, Leanne told cameras backstage: "I've never really gone on stage to sing.
"Something about that really kind of scares me. I can't bare the thought of just standing in front of everyone, all eyes on me. I'm worried about getting on stage and I won't be able to just get a note out."
She added: "I'm doing this for my son to teach him to be brave. I have to do this."
Stepping out on stage, Leanne introduced herself to the judges where she opened up about being a survivor of the Grenfell Tower Fire.
"I just made a decision that I'm going to do something positive and try to make something positive out of something negative," she said of her decision to audition for BGT.
For her audition, Leanne performed Sam Smith's Lay Me Down.
You can watch Leanne Mya's Britain's Got Talent audition in the video above.
Afterwards, David said: "It's very rare that you see a singer so committed to meaning every single word they say. Obviously the story is one that touched everyone around the world. You did something extraordinary today. You should be proud."
Alesha added: "Really great song choice. I was holding on to every single word you were singing. You created this beautiful atmosphere in the room. It was lovely."
Amanda commented: "You were so terrified and so nervous but you delivered that song with such a quiet confidence. It was stunning."
Simon concluded: "I think this is very important what you just did. I'm actually surprised every year at how many amazing people we meet on this show who have the courage like you to share something. I love things that do make a difference. And that was really special."
Plus there was young magician Dan Rhodes who 'cut' Amanda in half and singer Jacob Jones who also used his audition to propose - fortunately the judges said yes to the performance and his girlfriend said yes to the proposal.
Britain's Got Talent auditions conclude next Saturday night on ITV from 8PM.
The live shows begin on Monday, May 27.