The Oscar-winning actor, who plays the former Prime Minister's husband Dennis in The Iron Lady, revealed that he was pleased when she left office in 1990.
"I never was a great Thatcher fan and it wasn't a sad day in my life when she resigned," Broadbent told The Daily Telegraph.
However, the 62-year-old confessed that the nature of Phyllida Lloyd's biopic allowed him to view Thatcher in a "sympathetic" way.
Broadbent added: "When you research someone, you actually get beyond your own preconceptions and become aware of the human being other than the image. You become empathetic and sympathetic in turn."
Actress Meryl Streep's humane portrayal of the Conservative leader has prompted mixed reviews from critics and those who knew her.
> Jim Broadbent: 'I would've chosen less controversial roles'
> Meryl Streep: 'I had second thoughts about Margaret Thatcher role'
Watch the trailer for The Iron Lady below: