The Hunger Games star made the revelation in a recent interview with the UK's The Independent newspaper, and admitted that he wished he was able to do a similar generous gesture.
Chris Hemsworth, star of the huge Marvel movie franchises Thor and Avengers, called his father out of the blue one day and simply told him to check his bank account.
Liam says, "(My father) called my brother Chris back and said, 'I don't know how to feel. Since I left home, I have had debts and I thought I'd be paying them off until I died and have this weight hanging over me, and now to have them completely cleared.'
"They are so happy now and able to spend more time with us. I would love to be able to do something for my parents like that."
The Aussie actor, who plays Gale Hawthorne in The Hunger Games, opposite Jennifer Lawrence and Josh Hutcherson, is estimated to be worth around $82 million (£51.6 million), according to editors at MailOnline.com.
Liam also revealed that while he would love to make a film with his older brothers Chris and Luke, he it would be "so difficult" due to his siblings and their pranks.
"We have talked about it for a long time. I don't know what the movie will be, but possibly we will only get one chance to do it. We are waiting for the perfect thing," he says.
"When I was 17, I did one episode of a show with my eldest brother Luke. It was a kids' fantasy TV series, and it was the hardest day on set I've ever had in my life, because if he wasn't on camera, he would be doing something that was just trying to ruin me while I was on camera. And so I think it would be so difficult to make a film with my brother."