The long-in-development adaptation of Hunter S. Thompson's novel stars Johnny Depp in the lead role with Heard playing his love interest.
Heard told Metro: "I was a fan of the book written by Hunter S. Thompson and also Bruce Robinson, who directed it. Working with Johnny Depp was also certainly a plus. I knew the integrity of the material would be protected."
Asked how the movie might change her career, she added: "I've done all sorts of movies and it's hard to be objective about where you are in terms of the films you make. Every film I've done has been a step up.
"I worked my way up from the bottom and had to work up from being an extra, to a small part, to a one-liner, to where I am today. I hope The Rum Diary gets all the attention and accolades it deserves but it's hard to tell before it's released."
Of working with Johnny Depp, Heard said: "He has a personal connection with Hunter S. Thompson and carried that with him when we filmed. It felt like I was working with someone who really had a special understanding of the material."
> Click here to watch our recent interview with Amber Heard