An anonymous private collector made the winning bid, Heritage Auctions said.
The chair is one of four mismatched chairs given to the then little-known writer for her flat in Edinburgh, Scotland, and which she used while writing "Harry Potter and the Sorcerer's Stone" and "Harry Potter and the Chamber of Secrets."
The seller, Gerald Gray, of Worsley, England, said the winning bid far exceeded his expectations.
The unassuming 1930s-era oak chair with a replacement burlap seat decorated with a red thistle sat in front of Rowling's typewriter when she was "writing two of the most important books of the modern era," said James Gannon, director of rare books at Heritage Auctions.
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"I plan to donate 10 per cent to JK Rowling's charity, Lumos, because that's what she did in the first place," said Gray, a businessman who runs an automobile speed control equipment company in Manchester, England, and in Sarasota, Florida, called AutoKontrol.
He said he would like to see the new buyer display it somewhere where children could see it, perhaps in a museum or theme park.
He bought the chair in 2009 after his daughter, a Harry Potter fan, saw it on eBay.
She also signed the backrest in gold and rose colours and wrote "I wrote/Harry Potter/while sitting/on this chair" on the seat.
The word "Gryffindor," the Hogwarts house of Harry, Hermione Granger and Ron Weasley, is spelled out on a cross stretcher.
The chair is accompanied by an original typed and signed letter Rowling wrote prior to the first auction.
My nostalgic side is quite sad to see it go, but my back isn't. JK Rowling.