The "Silence of the Lambs" star wore padding and facial prosthetics to transform into the portly, smartly-dressed director for the film but refused to pile on weight for the role, reported Daily Express.
He also insisted on turning up to rehearsals alongside co-stars Helen Mirren and Scarlett Johansson in formal clothes to perfect his portrayal of the cinema icon.
"I spent about an hour and half in make-up each day. I also shaved my head, because I'm quite gray and Hitchcock used dye - that awful red dye. And then, once you get into the mask, I'm not Alfred Hitchcock; I'm Anthony Hopkins playing the guy.
"So I used what I could. I wouldn't go on the set till I was completely dressed. I wouldn't go on in jeans, even in rehearsal. If you're going to rehearse a scene, become the character. I wanted to feel the illusion of what I was trying to do, and that's what I did," he said.
The film, directed by Sacha Gervasi, focuses on Hitchcock's relationship with his wife Alma Reville and how they struggled to finance 'Psycho', which went on to become one of his most successful films.