The Misfits star told SFX that he has won a "guest lead part" in the period drama.
"I'm shooting in Dublin," Gilgun confirmed. "[It's] f**king so ace, I can't even tell you, I've grown a moustache and everything. It's epic, it's grown over my lip and I can curl it. I look like Charles Bronson after a famine."
The actor added that he is "bloody thrilled" to have won a role in the eight-part series, which stars Matthew Macfadyen.
"It's set in the time of Jack the Ripper," he said. "It's a guest lead part so I'm bloody thrilled with it. It's just such a bloody great job."
Set in 1899 London, Ripper Street will focus on H Division, the notorious police precinct charged with keeping order in Whitechapel.
Jerome Flynn (Game of Thrones), Adam Rothenberg (Alcatraz) and MyAnna Buring (Twilight) will also star in the project, written by Mistresses scribe Richard Warlow.
Shooting on Ripper Street is expected to conclude in July. The series will air on BBC One in the UK and on BBC America in the US.
> Misfits star Joe Gilgun: 'Series four will be completely outrageous'