Speaking to Crave Online, the actor - who played Sandy Cohen on the teen drama from 2003 to 2007 - admitted that he was excited by the pair's grounded style of storytelling.
"I was drawn to working with Dave and Doug again," he said. "I like the way they tell stories, because they’re powerful storytellers and they like to have the story they tell find a place in the world we live in."
Gallagher explained that his character on Covert Affairs, CIA director Arthur Campbell, is motivated by a strong sense of duty.
"I think he honestly believes that what he does is important," he said. "I think he’s very patriotic. I think he cares a lot for the country and I think he cares a lot for the people under him. I think that’s what gets him out of bed.
"I think he honestly believes that what he does and what the Agency does is important and that, like all large organisations, it’s not perfect and he likes the challenge."
He also revealed that Campbell's relationship with Piper Perabo's character Annie Walker will develop as the show continues.
"[Arthur] is becoming very much aware of this very young and very valuable asset, Piper. So she obviously has his attention and, judging from the last episode I shot, his respect. So I think it’s an open relationship."
The actor previously said that he enjoys his character's on-screen romance with wife Joan (played by Kari Matchett).
Covert Affairs premieres on July 13 at 10/9c on USA.