Stepping out in front of a throng of fans who braved the wind and rain outside the BFI in London, Streep spoke of how she had wanted to unravel the 'human side' of Britain's former premier.
"I consider all the roles I play a privilege but this one was special because there are such vehement opinions about her," she said.
Meryl Streep with Jim Broadbent, who plays Denis Thatcher
"People seemed to look at her as an icon or a monster and I just wanted to locate the human being inside those caricatures that we've seen over so many years. And to investigate myself what it must have been like for her."
Alongside Streep, fellow stars Jim Broadbent, Richard E. Grant and Olivia Colman also turned out for the film's premiere, which has been tipped for success at the Oscar's.
If Streep were to win an Academy Award for her role, the 62-year-old admitted she would find it just as much an honour as her previous two victories.
"It would be great, because the secret of the nomination is that it comes from the actors and actors are the ones who know what you go through. So it would be amazing," she said.