Independence Day star Pullman will play child killer Oswald Danes in the ten-part sci-fi drama, while Barrowman will reprise his role as Captain Jack Harkness.
Referencing Pullman's Independence Day role, Barrowman told TV Choice: "I was very nervous, but became very excited because I was going to be standing in a little room with the President of the United States."
He added: "When you're filming, you don't really have time to think about it. You just get up and do it, [but] who would ever have thought I would be on a TV show with Bill?"
Barrowman also revealed that Captain Jack has an "interesting" connection with Pullman's deranged character.
"The first time Jack sees Oswald is on television," he revealed. "Jack's sitting by the computer doing some research and he sees him on a talk show.
"Every time this miracle is mentioned, Oswald pops up. So if that happens, [Jack] deduces that he has something to do with it. It's very interesting the way the path turns and changes."
Torchwood: Miracle Day begins on Friday July 8 at 10pm on Starz in the US and on Thursday July 14 at 9pm on BBC One in the UK.
> Torchwood: Miracle Day: Bill Pullman video interview
Watch John Barrowman discuss Torchwood: Miracle Day with Digital Spy below: