The toilet, by Maurizio Cattelan - the provocative Italian artist known for taping a banana to a wall - went up for auction Tuesday evening at Sotheby's in New York.
The starting bid for the 101kg, 18-karat-gold work was about $US10 million ($A15 million).
Cattelan has said the piece, titled 'America', satirises super wealth.
"Whatever you eat, a $200 lunch or a $2 hot dog, the results are the same, toilet-wise," he once said. Sotheby's, for its part, calls the commode an "incisive commentary on the collision of artistic production and commodity value".
Klimt's 'Portrait of Elisabeth Lederer' sold earlier in the night after a 20-minute bidding war, also becoming the most expensive work of art ever sold by Sotheby's worldwide.
The portrait was one of the few by the Austrian artist that survived World War II intact. It depicts the young daughter of one of Klimt's patrons and was kept separate from his other paintings that burned in a fire at an Austrian castle.
The piece was part of the collection of billionaire Leonard A Lauder, heir to cosmetics giant The Estée Lauder Companies. He died earlier this year.
The toilet, which had been owned by an unnamed collector, was one of two that Cattelan created in 2016.
The other one was displayed in 2016 at New York's Guggenheim Museum, which pointedly offered to lend it to US President Donald Trump when he asked to borrow a Van Gogh painting.
Then the piece was stolen while on display in England at Blenheim Palace, the country manor where Winston Churchill was born.
Two men were convicted in the toilet heist, but it's unclear what they did with the loo. Investigators believe it probably was broken up and melted down.
