JK Rowling, the book's author, was an unemployed single mother without a publisher or agent 13 years ago.
However, she is now the world's first billionaire [US$] writer after the huge success of her first six novels and the Hollywood movies based on them.
But the latest release has been marred by a number of leaks of the contents of the book on the internet, both real and fake.
In addition, a mistake made by a US online retailer allowed a small number of hard copies to be sent to buyers days ahead of publication.
Rowling, 41, reacted angrily when two US newspapers ran reviews on Thursday based on copies they had obtained ahead of publication.
She said: "I am staggered that some American newspapers have decided to publish purported spoilers in the form of reviews in complete disregard of the wishes of literally millions of readers, particularly children."
On Friday, Le Parisien, the French newspaper, published a three-paragraph summary of the book's epilogue, printing it upside down to give readers a chance to look away.
However, Potter's publishers will take comfort from the fact that the majority of fans do not know what happens in book seven, and do not want to until they get their hands on a copy on what has been dubbed in the media as 'P-Day'.
Families are imposing news blackouts in their homes, and queues began to form outside bookstores as early as Wednesday.
More than 100 die-hard Potter fans, including several from overseas, had gathered outside one book shop in central London on Friday, braving torrential rain at one point.
Sinead Kelly, who travelled from the Netherlands with her boyfriend to be there, said: "Everyone says he [Harry] is going to die. I think he's going to live.
"JK Rowling says at least two characters are going to die, so I think it's going to be Hermione and Hagrid."
In Britain, a phone counselling service for children expects a surge in calls when readers learn who is killed off.
Stores in Taiwan and India are laying on 'magic breakfasts' for early customers and a Sydney shop is taking fans aged from two to 84 on a train ride to a secret location to get the book.
The first six books in the series, which began with Harry Potter and the Philosopher's Stone in 1997, have sold 325 million copies and the first five movies in the film franchise have amassed around $4bn at the global box office.
Caroline Horn, a children's news editor at the publication Bookseller, said: "Harry Potter has made people look at the children's book world in a way they wouldn't have before.
"It also raised expectations of the amount of money a writer can earn."