The award-winning actress explained that she was initially frightened to play such an iconic figure, but soon learned that she and Thatcher shared some common ground.
"It was extremely daunting, because I'm from New Jersey," she joked to The AP. "And yet as an outsider, I felt something of what she might have felt."
Streep's performance and the film itself have received mixed reviews from critics and members of Thatcher's inner-circle, but the actress is quick to mention that The Iron Lady is not a traditional biopic.
"I was interested in it precisely because it wasn't really [a biopic]… It's a subjective imagining," she insisted. "It's not the God's-eye-view chronicling this side, that side, the politics of it. It's a very deep look at a whole life - from the end of it."
Streep's co-star Jim Broadbent recently revealed that he has never been a Thatcher supporter, but gained sympathy for her while shooting The Iron Lady.
The Iron Lady is now playing in the UK and on limited release in the US. The movie opens wider in the US on Friday, January 13.
> Iron Lady Q&A: If Meryl Streep's not Oscar nominated there'll be questions
> Meryl Streep: 'I had second thoughts about Margaret Thatcher role'
Watch the trailer for The Iron Lady below: