Niamh Cusack: 'I thought I'd missed my chance to play Lady Macbeth'

Niamh Cusack first appeared as Desdemona in Othello at the RSC back in 1985, and went on to perform in two seasons back-to-back at the venue over the next two years including starring opposite Sean Bean as Juliet in Romeo and Juliet. She later originated the role of Siobhan in Simon Stephen's Olivier Award-winning stage adaptation of The Curious Incident of the Dog in the Night-Time, and was also nominated for a WhatsOnStage Award for her performance in Playboy of the Western World at the Old Vic.

She now returns to Stratford to play Lady Macbeth in the venue's new adaptation of Macbeth, opposite Christopher Eccleston. Directed by Polly Findlay (Beginning), the show, which opens this month sees the murderous couple claim the throne through a bloody plot.

I never thought I'd get the chance to play Lady Macbeth. I was talking to Polly Findlay last year and told her I thought my time had gone to play the part. Three months later she called me and asked me if I wanted to star in the show opposite Christopher Eccleston at the RSC. I said yes straight away.

Polly's production reminds us that anyone could become the Macbeths. There're no mobile phones or laptops but there's something very modern about the play. The Macbeths are not monsters, they've just lost their children. They're wounded and damaged. Life B is to be King and Queen, as opposed to Life A, which was to be a couple with children who lived.

Christopher Eccleston is a theatre animal. A lot of my performance relies on having a great Macbeth, and Christopher has such a rich quality within himself. He speaks the verse like he's making it up as he's going along. It just sounds so natural.

It's my first time back at the RSC in quite a while. My son was two last time I was there (playing Rosalind in As You Like It) and now he's in his 20s. I've always wanted to come back and I'm thrilled that this piece of luck has landed in my lap. There's a wonderful and collaborative atmosphere within the building and a lot of women within the creative team of Macbeth – the designer and the lighting designer are women and the entire stage management team are women.

I went for coffee with my sister Sinead to discuss the part. She played the same role of Lady Macbeth back in 1986 opposite Jonathan Pryce, so we had a chat about it. It was useful, but I do think a lot of the part depends on your director's vision. I've seen some brilliant Lady Ms – Harriet Walter and Bríd Brennan were great.

One of my most embarrassing moments was during my first RSC appearance. I was chatting in the wings with the wonderful actress Janet Dale who played Amelia, while Cassio was introducing me on stage. He said "Behold, here comes Desdemona!" and there was no Desdemona to be seen. I was still in the wings having a chat. It was only a few seconds but it felt like an eternity. I hope I don't do that this time around.

My dream role would be in Long Day's Journey Into Night. Although there's a wonderful production of that in the West End right now with my brother-in-law in the lead role, alongside the marvellous Lesley Manville. Give me a few years and I'd love to do that. I'd love to be Hecuba as well.

Macbeth runs from 20 March to 18 September with previews from 13 March.