This Is Us star says show brings answers

This Is Us star Justin Hartley thinks if you don't cry watching the TV drama, there's something wrong with you.

The US TV series is renowned for pulling on its viewers' heartstrings. On paper, it's a simple family drama but it's made complex by its use of flashbacks and time hops which explore how much a person's past affects so much of their present.

"We've read the script, we've shot the scenes and know exactly what's going to happen and still you find yourself getting emotional," Hartley told AAP.

"I actually worry about people, they're very few and far between, but people who are like 'yeah I watch the show, I never cry when I watch the show'. I feel a little bit like, not that I'm a doctor, but I feel like they need one. Like 'you need to go talk to somebody, crack that cold heart open'."

The show has been a massive hit, pulling in viewers around the world and winning awards including a recent SAG Award for Outstanding Performance by an Ensemble in a Drama Series.

Hartley plays Kevin, one of three Pearson siblings whose parents Jack and Rebecca are played by Milo Ventimiglia and Mandy Moore.

Unlike other dramas that rely on will-they won't-they romances, viewers of This Is Us have been waiting to find out how Jack dies. His death was revealed early on in the first season, but Hartley says it was never part of a strategy to keep the audience hooked.

"The way it happens is very much in keeping with that awesome storytelling where it keeps you on the edge of your seat with sort of a twist at the end," he explains.