Pitt confronted Weinstein after Paltrow told him about the encounter, but the producer warned Paltrow not to tell anyone else about the incident.
The 45-year-old actress told "The Howard Stern Show" on Wednesday she was "blindsided".
Paltrow said her boyfriend-of-the-time "leveraged his fame and power" to defend her and she adores him for that.
After she was hired for the 1996 film "Emma", Paltrow was called into a meeting in the media mogul's hotel room in Beverly Hills.
In an unprecedented domino effect, as many as 70 women - including Ashley Judd, Cara Delevingne, Kate Beckinsale and more - accused Weinstein of sexual harassment and rape.
When Stern asked Paltrow if she approved of Pitt's actions, she responded enthusiastically. "I told [Pitt] right away and I was very shaken by the whole thing, and I had signed up to do two movies with [Weinstein]", she said. "We were at the opening of "Hamlet" on Broadway that Ralph Fiennes was in and Brad Pitt was there. We're on the same team", she says, adding the "American Horror Story" producer is "fantastic" with her two kids, Apple, 14, and Moses, 12, but admits it's not always an easy family adjustment. Weinstein had suggested that they go get massages in his bedroom. Her boyfriend at the time, however, was Brad Pitt, who did already have clout in Hollywood. And I think that Brad is somebody who is extremely, really intelligent, and he's very emotionally intelligent, and I think he's a really good person to try this with. The Manhattan district attorney's office is expected to charge Weinstein Friday regarding a case involving allegations of forced oral sex from Lucia Evans.