The singer took to Twitter to share the news with her fans yesterday (September 22).
"The reaction to FAME has been overwhelming," she posted. "6 million bottles in 1 week makes it the 2nd fastest selling fragrance after Coco Chanel."
'Fame' - produced by Coty - was initially released in Macy's and UK stores on August 22, but a worldwide launch followed on September 1. A huge marketing campaign accompanied the launch, including billboard posters, multiple TV spots shot by Stephen Klein and personal appearances by GaGa herself.
The star had previously claimed that it would carry the scent of "blood and semen", but according to promotional materials, the fragrance combines notes of atropa belladonna, tiger orchid, incense, apricot and saffron.
The packaging describes it as "the world's first black eau de parfum", which becomes invisible once airborne.
Last night, Lady GaGa played to a crowd of 75,000 at Paris's Stade de France as part of her 'Born This Way Ball' tour. She had previously been spotted bulging out of her tight-fitting costumes and told radio host Elvis Duran that her fuller figure was a result of her dad's cooking.
"I love eating pasta and I'm a New York Italian girl," she said. "That's why I have been staying out of New York.
"My father opened a restaurant. It's so amazing... it's so freaking delicious, but I'm telling you I gain five pounds every time I go there."
She added: "I'm dieting now but my God, I think I gained, like, 25 pounds (1.8 stone) over Christmas."
Watch the full promotional film for 'Fame' by Lady GaGa below: