The 'Poker Face' singer, 29, describes how she blamed herself for the attack 10 years ago and how she kept it a secret from everyone close to her.
Speaking about the ordeal at a New York Times' TimesTalks event on Thursday (10 December), Lady Gaga - real name Stefani Joanne Angelina Germanotta - said: "I didn't tell anyone for I think seven years. I didn't know how to think about it.
"I didn't know how to accept it. I didn't know how to not blame myself or think it was my fault. It's something that really changed my life. It changed who I was completely. It changed my body, it changed my thoughts."
The American Horror Story actress, who was assaulted when she was 19, continued: "When you go through a trauma like that, it doesn't just have the immediate physical ramifications. For many people it has almost like trauma, where you re-experience it through the years after it.
"It can trigger patterns in your body of physical distress. So a lot of people suffer not just emotional and mental pain, but physical pain as a result of being abused, raped or traumatized in some way."
Appearing on a panel, Lady Gaga sat alongside Kirby Dick, the writer/director of documentary The Hunting Ground, which investigates the issue of sexual assault on US college campuses.
The singer's song 'Till It Happens To You' appears on the hard-hitting documentary as a tribute to those who have been sexually assaulted.
She and co-writer of the song Diane Warren said they wanted the song to show people who have been assaulted that it's "okay to feel this way" and that they are "not a victim".
Lady Gaga adds: "You can own your pain. It can be a good part of you."
The day after the event, the star performed 'Til It Happens to You' at Billboard's 10th Annual Women in Music luncheon at Cipriani in New York, where she was named Billboard's Woman of the Year.
She was joined by her fiance Taylor Kinney at the prestigious event.
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