As she reads, fans across the globe anticipate the joy of reading their own copies.
"Oh, my God, I can't even believe I can go back to the hotel room and read this," said one fan. "I can read this, I can read 'Harry Potter!'"
In London, from 12:20 a.m. until 7 a.m., Rowling signs 1,700 copies of her book.
"Does it really matter now if I get a bit drunk and disorderly?" she says. "I've finished the books."
In the first 24 hours after publication, 2.65 million books are bought in the United Kingdom and 8.3 million books are sold in the United States -- that's over 7,000 copies a minute.
Rowling talked about how she finished the series.
"In some ways it would have been a neat ending to kill [Harry], a neater ending to kill him," she said, "but I felt it would have been a betrayal because I wanted my hero -- and he is my hero -- to do what I think is the most noble thing, so he came back from war and he tried to build a better world, I suppose, corny as that sounds, both on a small scale for a family and a larger scale."
But might there be another "Harry Potter" after "Deathly Hallows"?
"I think no, it's definitely time to stop, it's time to stop now," said Rowling. "It gives me a certain satisfaction to say what I thought happened, and to tell other people that, because I would like my version to be the official version still, even though I've not written it in a book. 'Cause it's my world. But no, I don't want to write anymore Hogwarts books."
Instead, Rowling said, she is focusing on family life.
"I'm making David's birthday cake 'cause he's 4 tomorrow," she said about her son, "but it's just the family tea birthday cake, 'cause the day after that we have the party for all his friends and then he gets a shop-made Lightning McQueen from the Disney Pixar film with which he is obsessed.
"Baking really reminds me of my mother, 'cause she made fantastic cakes, so that really makes me feel like I'm doing the proper motherly thing when I'm making birthday cakes -- and David really likes my cakes particularly."
These days, Rowling is trying to balance two parts of her life -- a family life as normal as she can make it, and a public life with millions of fans and million-dollar deals, such as a planned "Harry Potter" amusement park.
There's also the question of money. According to some press reports, Rowling has amassed 570 million pounds -- almost $1 billion.
"Those reports are bollocks," said Rowling. She said she has "loads, but I'm not telling you how much ... but it's definitely not 570 million. ... I think it's private."
Rowling has given away millions of dollars. But she has never forgotten what it was like to have very little money. She made a visit with Runcie to the small apartment in Leith where she finished the first "Harry Potter" book, before success hit.
"This is really where I turned my life around completely," she said. "My life changed so much in this flat.
"I feel I really became myself here in that everything was stripped away, I had made such a mess of things, but that was all, that was freeing, so I just thought, 'well, I want to write, so I'll write the book and what, what is the worst that can happen, it gets turned down by every publisher in Britain, big deal.'"
What is she working on now?