The series follows an extended family: siblings Kate (Chrissy Metz) and Kevin (Justin Hartley), their adopted brother Randall (Sterling K. Brown), mother Rebecca (Mandy Moore) and father Jack (Milo Ventimiglia).

The series was initially assembled "off cycle", which means it was not part of LA's traditional pilot season. It was also parked at a US network that does not have a strong track record for edgy drama, NBC, more commonly the home of very formulaic procedurals and safe network comedies.

"You're kind of like, all right, off cycle for NBC, huh? That's an interesting proposal," Ventimiglia tells Fairfax Media. "Then you start reading the names behind it. Dan Fogelman, John Requa, Glenn Ficarra. These are significant filmmakers. These are guys that you hear about, and you want to work with."

Having read the script, Ventimiglia was immediately determined to get into the room to meet with the producers.

"The first thing is just how incredibly inventive it was, you know," he says. "And at the end [of the pilot script] one of those beautiful moments in storytelling where you didn't see it coming. Honestly, I didn't see it coming."

The series does use one unusual narrative wrinkle – mild spoiler in a moment – in that Ventimiglia's character Jack is dead, and features in flashback scenes with his on-screen wife Rebecca (Mandy Moore). As a result, the show's storylines are set either in the present, or in the late 1980s.

To some extent it is a narrative red herring; though he may be dead – the details and date of which are yet to properly unfurl themselves – Jack is, in some respects, the star of the show.

"I think people are looking at his decisions in his life, and the way he approaches everything, knowing that," Ventimiglia says. "You're watching a dead man, but at the same time, here's a guy, who very simply loves his wife, loves his family, and he does everything he can for them."

Ventimiglia found the notion compelling when he read the script.

"Clever is the wrong word, I think it's a very wise choice to have Jack no longer be in the picture because I think it adds many layers to each of these characters," he says. "From his children to his wife, it gives him a level of humanity that they maybe wouldn't be able to play with, if Jack was still around."

Ventimiglia notes that he does know the date and detail of Jack's death, though that remains a mystery as the show goes into its second season in the US and fans of the series continue to feverishly discuss it.

"I know all of that, I know exactly where it happens, I know when it happens," he says. "The good news is, even if you take that end date, and you mathematically map out how many days this man had lived up until that date, I think there's still a ton of stories that you can mine within that world."

From Ventimiglia's perspective there is another unusual wrinkle: though the show is an ensemble, he works mostly with Moore.

"I'd like to work with everyone in the cast, at the same time I think it's a nice balance, because television production is a tough schedule," he says.

"Justin, Sterling and Chrissy aren't working on the days that I'm going to be working, they get a break. Same thing, vice-a-versa for me. Mandy is the only one whose kind of in the middle of all of that and works her ass off all the time."

The most striking aspect of the series is its gentle realism, a trait it shares with fewer television programs than you might imagine. Thirtysomething and Love My Way spring to mind here, as shows that buck the less realistic "television reality" that permeates most programs.

"I think the realism is part of what makes it relatable," Ventimiglia says. "Nobody really strives to watch anything that's unauthentic. The second that you see that something is unauthentic, maybe a smarter viewer is going to decide that it's not for them.

"Any of these characters could be your neighbour, could be your friend, could be someone that you do be business with, anything."

The series has won a two-season renewal, which takes it to the end of a third season in 2018, a powerful statement of artistic intent from NBC in a modern television economy that is less forgiving of programs which are not either shamelessly mainstream or commercially strong.

"It gives a confidence to the viewer, it gives a confidence to the production group," Ventimiglia says. "It's something that is allowing us on the creative end to commit in a way that a lot of people don't get."

WHAT This Is Us

WHEN Ten, 8.30pm