Earlier this year, Cillian Sullivan starred as Bobby O’Brien in new feature film Spilt Milk, which had a cinema release in Ireland, and he has just finished filming for an upcoming feature film – Silverback – which stars Tom Vaughan-Lawlor and Jason Isaacs. Cillian played Stevie Sondheim in the 2025 film Blue Moon, which had a cast including Ethan Hawke as Lorenz Hart and Simon Delaney as Oscar Hammerstein II and was directed by Richard Linklater, with the film having huge success for its release, with nominations at the 2026 Oscars, Critics Choice Awards, Golden Globes and BAFTAs. Two short films that Cillian has worked on – The Things We Do and A Song – premiered at Galway Film Festival last year, and as a voice actor, he voiced PJ in the animated short No Worries!, which was part of RTÉ Kids Sparks: School’s Out scheme, and he recorded the titular characters in Little Caesar and Sullivan’s Sails. Speaking with Cillian, we found out from him about this year’s release of Spilt Milk (in which he starred as Bobby O’Brien), filming as Stevie Sondheim in Blue Moon and his voiceover work.

What was it like on set of the new feature film Spilt Milk and was there anything that drew you to the project?

I had such an amazing time filming Spilt Milk. There was a big cast, which meant I got the chance to learn from and work alongside so many talented Irish actors every day. I was absolutely delighted to be cast as Bobby, and what really drew me to the project was the story and the people behind it. It felt like something special from the start.

How was it starring as lead character Bobby O’Brien and what did you enjoy most about the role?

It was such a great experience getting to play a lead role in a story set in the 80s. It’s not a time I’m familiar with, so playing Bobby meant I had to really use my imagination and do a bit of research to understand the world he was living in. What I enjoyed most was being able to step into a completely different era and figure out how Bobby would speak and react to everything around him.

Can you tell us about Spilt Milk, and how does it feel now the film has released in cinemas in Ireland?

It was such an honour to work with everyone in the cast and crew, so seeing the film released in Irish cinemas was really exciting. It can be strange seeing yourself on the big screen, but it’s also a brilliant feeling to watch the whole story come together and hear how audiences respond. We did a few festivals in the run-up to the cinema release, and the reactions were really positive. We won some awards too along the way, making the whole experience even more special.

You portrayed Stevie Sondheim in last year’s film Blue Moon; how was it taking on the character?

This was another great opportunity for me. Taking on Stevie Sondheim meant stepping into the world of someone so well known, while also trying to portray him when younger. I wanted to make him feel real, so I focused on who he was at that stage of his life and what might have shaped him.

How did you prepare for playing Stevie and how familiar were you with Stephen Sondheim before booking Blue Moon?

To prepare, I read up on who Stephen Sondheim was and looked into his childhood so I could better understand what he might have been like, and also how he knew Oscar Hammerstein. Before being cast in Blue Moon, I didn’t know a huge amount about him, but once I started listening to his work and learning more about his life, I understood why he is such an important figure and why he was included in the script.

What were your scenes like to film and how was it working with Ethan Hawke (who stars as Lorenz Hart), Simon Delaney (Oscar Hammerstein II) and director Richard Linklater?

Filming the scenes was a great learning experience because the set was really focused and professional, but also very relaxed and supportive. Working with Ethan Hawke, Simon Delaney, and all the cast was brilliant. They’re all incredibly experienced and generous, and I learned so much from watching how they approached each scene. Richard Linklater was also amazing to work with. He gave really clear direction while still letting me play the role the way I had interpreted it, which made for an amazing experience.

How has it been seeing the huge success to Blue Moon and having it be nominated at ceremonies including the 2026 Oscars, Critics’ Choice Awards, Golden Globes and BAFTAs?

It’s been surreal, to be honest. When you’re filming, you’re just focused on doing your best, so seeing the response afterwards was exciting. The nominations and attention around the film were a huge honour for everyone involved, and it’s been lovely to see the hard work from the whole cast and crew recognised. Ethan put so much into playing Larry that he truly deserved all the recognition he received.

Can you say about your time involved with the short films The Things We Do and A Song?

I filmed The Things We Do in Wexford a few weeks after Blue Moon, so it was a busy time, but I loved it. There was another wonderful cast of Irish actors, and the atmosphere on set was really friendly. Short films are great because you get to tell a full story in a short space of time. Working on A Song was similar in that way too. It was really creative, and a great experience overall. Both short films premiered at the Galway Film Festival last summer.

What was it like voicing PJ in the animated short No Worries!, which was part of the RTÉ Kids Sparks: School’s Out scheme?

This was a really fun project to be a part of, and it also had a meaningful theme for kids experiencing anxiety. We all met in a Dublin studio and recorded together, so there was a great buzz on the day. Voice work is always enjoyable because you get to play around with different sounds and choices, and everyone involved made it a really relaxed and enjoyable session.

How was the experience recording for Little Caesar and Sullivan’s Sails as the titular characters?

Sullivan’s Sails was recorded over a few months, so I really got time to settle into the character. It was a fun and beautiful animation to be a part of. It was great to then see it air on TV. Little Caesar was great fun too, and has had great success at animation festivals. Recording can be intense in a different way to filming, but it’s also really enjoyable.

How different do you find voiceovers opposed to filming for screen?

Voiceover work is a bit different because you don’t have the costume, set, or camera there to help tell the story – it is all with your voice. In some ways, it can feel easier because you’re not on screen, but it can also be tricky to find the right sound and keep it consistent. I usually try a few different options, listen back, and then stick with what feels most natural for the character.

Where does your love of acting come from and how did you get into it?

When I was really young, I loved putting on different voices for my toys and copying characters I saw on TV. When I was five, my parents brought me to a drama class – Talented Kids in Co. Kildare – and I just really enjoyed it from the very beginning. Acting happened a bit by accident after that. I went for a few auditions, got cast in some educational campaigns, and it all started from there.

Have you received any advice over your time as an actor so far that has stuck with you?

The best advice I’ve received has come from my parents, in relation to submitting self-tapes and doing auditions. They have always encouraged me to focus on doing my best and to trust that, if a role is right for me, it will come my way. If it doesn’t, to not take it personally.

Do you have any favourite films and TV shows to watch?

I love Stranger Things. It has been one of my favourite shows in the last while.

How do you like to spend your free time?

I play a lot of sport. I play football and rugby, so I spend a lot of my free time training during the week and playing matches at the weekends.

What are you hoping this year brings for you, and do you have any projects coming up that you can tell us about?

I have just finished filming a new feature film called Silverback, starring Tom Vaughan-Lawlor and Jason Isaacs. It was another exciting project, and I can’t wait for it to be released.

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