The Star Trek actor will play a recurring role in the sci-fi drama, it was announced in April.
"I'm a recurring character in the final three episodes of the series," he told SFX. "My character is CIA, very gruff, [and] unimpressed by the 'Torchwood clowns' as he'd call them."
De Lancie, best known for his role as Q in the Star Trek franchise, added that the new season of Torchwood still has a "British" feel.
"My sense is the show is still quite British," he said. "It has, mostly, an American crew, but the sensibility of it, led by Russell [T Davies], is very British."
He also claimed that Miracle Day is "completely different... to Star Trek" and that his role involved "no technobabble".
"It's someone's future, potentially real," he explained. "I enjoyed that."
Torchwood: Miracle Day will air in July on BBC One in the UK and on Starz in the US.
> Torchwood: Miracle Day: New pictures
Watch the official trailer for Torchwood: Miracle Day below: