The British star said when she was growing up a teacher suggested acting as a way of "removing me from me".
Blunt said yesterday: "It was the most intuitive thing, and he was right: the only way I could speak fluently was to be someone else."
The 31-year-old actress, who stars alongside Tom Cruise in new film Edge of Tomorrow, said of her stutter: "It alienates you in some ways if you have trouble communicating.
"It wasn't that I got bullied horribly about it, although kids definitely had a go sometimes.
"It comes back if I'm tired or stressed."
Blunt also spoke warmly about her co-star Cruise, adding that the actor does not take himself seriously.