Gervasi told Life & Style that he was immensely proud to have cast Johansson as Janet Leigh and Biel as Vera Miles in his movie about the controversy surrounding Psycho.
"They're amazing... They're both extraordinarily beautiful and ridiculously talented, but they were very professional on set," the director explained.
Gervasi continued: "Scarlett took it incredibly seriously. She read all the books, she called Jamie Lee Curtis - Janet's daughter - she got all her facts right, she researched what she wore, what she would be smoking on set, like she knew every biographical detail."
The filmmaker also credited Biel with bringing "a kind of vigour" to her portrayal of Miles.
"Obviously they're big stars and extraordinarily beautiful, but as actresses on the set, they couldn't have brought more," he added.
Johansson recently admitted that it was a challenge to play an iconic film star such as Leigh.
Hitchcock is now playing in the US and hits the UK on February 8.
Watch the trailer below: