When Louis McCartney first stepped into the dark and twisted world of Henry Creel in the Netflix stage production of Stranger Things: The First Shadow, few could have predicted just how far it would take him. Now, the 21-year-old finds himself nominated for a Tony Award for Best Leading Actor in a Play – and firmly in the Broadway spotlight.

His portrayal of a troubled kid’s slow descent into madness – his professional stage debut – has already earned him the Critic’s Circle Award for Most Promising Newcomer, the Stage Debut Award for Best Performer in a Play and the Theatre World Award for Outstanding Broadway Debut Performance.

“I’ve got endless words and no words at all. I keep stumbling over them,” Louis, who trained at Dublin’s Bow Street Academy, told The New York Theatre Guide following the Tony nomination. “I’m so thankful. I’m honestly so ecstatic. To be in New York celebrating this is absolutely insane.”

The First Shadow – an official prequel to the sci-fi series which returns for its fifth and final season in November – had already broken box-office records in London’s West End before transferring to Broadway in March, with the Northern Irish actor reprising his role as main antagonist Henry Creel, aka Vecna.

Written by Kate Trefry from an original story by the Duffer Brothers, Jack Thorne and Trefry, the play takes the audience back to 1959 - 24 years before Will Byer’s disappearance in Season 1 – offering answers to some of the more pressing questions Season 4 left behind. First and foremost, the origin and source of power of Vecna.

“Our goal is to make you feel for Vecna, which is almost impossible,” Louis said in an earlier interview with Hot Press. “A lot of Henry came pretty naturally to me. I’m a smaller guy, so in school I learned to be strong in myself and that I don’t depend on others. I used a lot of that feeling, not so much emotional recall, more by placing myself in Henry’s shoes reimagining my life as a little boy, who doesn’t know what’s going on in his mind, who just wants to fit in, fall in love, do good in school and do good with their Mum and Dad.”

On June 8 when the Tony Awards air live from Radio City Music Hall, Louis is up against a formidable line-up including George Clooney (Good Night, and Good Luck), Cole Escola (Oh, Mary!), Jon Michael Hill (Purpose), Daniel Dae Kim (Yellow Face) and Harry Lennix (Purpose).

• Stranger Things: The First Shadow is currently playing Tuesday through Sunday at the Marquis Theatre, New York.