The showrunner told BBC America that the story of the sci-fi drama is "always the story of the companion".
"It's always their story," said Moffat. "It was Rose Tyler's (Billie Piper) story, it's Amy Pond's (Karen Gillan) story - the story of the time they knew the Doctor and how that began, how it developed and how it ended."
He continued: "The story begins again, not so much with the new Doctor, but with the new companion. The Doctor's the hero, but they're the main character."
Moffat also described the idea of the Doctor (Matt Smith) travelling alone as "depressing" and "unhealthy".
"I thought about the Doctor travelling on his own and it always faintly depresses me," he admitted.
"I'm not sure what he does on his own but I don't think it would be healthy. He's far too old and he's seen too much."
New Doctor Who companion Jenna-Louise Coleman was unveiled to the public last month.
The Titanic actress will make her debut in the BBC drama's 2012 Christmas special.
> Doctor Who films in Manhattan - behind-the-scenes pictures
Watch the trailer for the next series of Doctor Who below: