The star has been nominated for Best Actor at this year's Oscars for his lead role in the film.

But for years Matthew was more commonly associated with rom-coms and that was something he wanted to change.

"I've become more selfish, but in a healthy way, or at least that's what I think. I've stopped asking for permission and looking at my career from outside: now, all that matters is how I feel. My conscious decision was changing gear, in order to reactivate my relationship with my career," he explained to Vanity Fair Italia.

"Everything was fine, I was having fun and making money. Still, I was feeling too comfortable, life was too easy and I like it when things are a bit harder instead."

After his first son Levi was born in 2008 Matthew decided to stop working and "see what would happened".

Then he got the script for Dallas Buyers Club, a true-life tale about Ron Woodroof, an AIDS patient who began smuggling unapproved pharmaceutical drugs into Texas when he found them effective at improving his symptoms.

The film has transformed Matthew's career - he has already received this year's best actor Golden Globe and Critics' Choice Awards - and now he is more excited than ever to work.

"I am much stronger because I no longer depend on other people's judgements," he said. "Over the last two years things have changed in a way that when Monday comes and it's time to work, I jump out of the bed and can't wait to be on set, I look forward to it as if I was a kid waiting for a cake. And the more difficult the character, the happier I am. The challenge is what really motivates me."