The 45-year-old actress recalled on Wednesday's episode of The Howard Stern Show how Pitt confronted Weinstein after the producer sexually harassed her in a hotel room. Paltrow and Pitt were dating at the time.
"I told him right away and I was very shaken by the whole thing," Paltrow told host Howard Stern. "We were at the opening of Hamlet on Broadway. Harvey was there and Brad Pitt -- it was like the equivalent of throwing him against the wall, energetically."
"It was so fantastic. He leveraged his fame and power to protect me at a time when I didn't have fame or power yet," she said. "He said, 'If you ever make her feel uncomfortable again, I'll kill you.' Or something like that."
Paltrow told The New York Times in October that she met with Weinstein at his hotel room after landing the lead in Emma at age 22. She said the producer placed his hands on her and suggested they move to the bedroom for massages.
"I was a kid, I was signed up, I was petrified," the actress recalled.
Pitt confronted Weinstein after Paltrow told him about the encounter, but the producer warned Paltrow not to tell anyone else about the incident.
"I thought he was going to fire me," she recalled.