Wareing: Albert Square is surreal
The Essex-born actress has twice been nominated for a Bafta for her films It's A Free World and Fish Tank and starred in TV shows Luther and Inside Men.
But Kierston who has joined Albert Square as feisty Kirsty Branning - is starstruck appearing in her favourite soap.
She told Inside Soap magazine: "It was really weird shooting my first scene. I've done TV before, but EastEnders is a show that I've grown up with.
"Suddenly I'm on the Square and seeing iconic characters like Sharon - but now I know her as Tish (Letitia Dean) and we're friends!
"There was a moment a few weeks ago when I was in the Vic and June Brown (who plays Dot) walked in. It feels like I'm in my own television set!"
Kirsty, Max's secret wife, is set to stir up a lot of trouble in Albert Square.
Kierston said: "I'm not sure the audience is going to like Kirsty, but there needs to be someone who they can love to hate.
"I do like playing her, she's far from boring. I'm hoping that she's got plenty of fight scenes, b****y arguments and sobbing coming her way!"