She was among bidders who paid almost half a million pounds for items from the personal collection of Daphne Guinness which was sold at Christie's. The lots went for four times the original estimate.
Gaga is understood to have set a new high for a McQueen, bidding £85,250 in a sale which saw her facing rival bids from institutions and couture collectors from around the world. The record price was for an ivory silk tulle empire line gown, entitled The Girl Who Lived In The Tree.
Daphne was auctioning items from her personal collection to raise funds for the Isabella Blow Foundation, which she set up in memory of her friend to support emerging fashion talent.
Fashionista Isabella killed herself in 2007, and her own extensive wardrobe - sold to settle debts on her estate - was bought in its entirety by Daphne to keep it intact.
Chart-topping star Gaga has spoken of her admiration for the two in the past, saying: "Isabella and Daphne are two exceptional human beings, women, icons."
Alexander McQueen was found dead in his Mayfair apartment in February 2010, days before London Fashion Week. His suicide shocked the fashion industry.
Christie's confirmed that Gaga was a bidder but was unable to provide further details of the items she purchased. Bidders from 21 countries took part.
Daphne said: "I'm overwhelmed by how many bidders took part this evening and I'm particularly moved by Lady Gaga's support for the foundation. I like her very much, and it's lovely to see the nascent beginnings of something that may help other people."
The collection went for £467,800, including buyer's premium.