Rowling, who was an impoverished single mother living on benefits when she wrote the first of her seven books, netted around £170 million last year, bringing her total fortune to more than £560 million.
Her income is more than the combined annual earnings of the nine other best-selling writers on the list, including James Patterson (£26.7 million), Stephen King (£24 million) and Tom Clancy (£18.7 million).
Rowling's status as the world's highest paid author reflects the cult status of her novels, which have sold more than 375 million copies and been adapted for the big screen.
It also secures her transformation from a lone mother struggling to make ends meet to a global phenomenon.
The writer had just divorced her Portuguese husband and was living in a mouse-infested flat in Edinburgh when she started work on the first book, Harry Potter and The Philosopher's Stone.
Since then each new instalment of wizardry has created a shopping frenzy, with bleary-eyed children and adults camping outside stores across the world to snap up a copy.
Lacey Rose, who compiled the Forbes list, said that the adventures of Rowling's boy wizard "took the publishing by storm" 10 years ago.
"Once a single mother on welfare, Rowling can now claim best-selling status thanks to her Harry Potter franchise," she said. "Over on the big screen, her Potter franchise has already generated £2.5 billion at the worldwide box office and she still has three more flicks to come."
She added: "While the publishing industry has struggled to come up with a 'happily ever after" storyline in recent years, there's still plenty of money to be made in the business of books.
"Sure it isn't the success it once was - blame it on the economy, the web and the big-box stores - but the publishing industry's top earners still manage to turn pages of prose into piles of cash."
Rowling, a personal friend of Gordon Brown, recently courted controversy by donating £1 million to the Labour party.
She said that she was motivated by Labour's record on child poverty and was opposed to David Cameron's plan to give tax breaks to married couples.
Rowling is not the only multi-millionaire on the list from humble beginnings.
King, the American horror writer, was scraping by on a schoolteacher's salary before his novel Carrie came out in 1974.
Since then, he has written more than 40 books, selling more than 350 million copies around the world.
Other authors on the list include Danielle Steel (£16 million), the bodice-ripping romance author who has written more than 70 books, and John Grisham (£13 million), author of A Time to Kill and The Appeal.
Forbes list of top 10 authors and their earnings between June 1, 2007, and June 1, 2008
1 J K Rowling £160m
2 James Patterson £26.7m
3 Stephen King £24m
4 Tom Clancy £18.7m
5 Danielle Steel £16m
6 John Grisham £13m
6 Dean Koontz £13m
8 Ken Follett £10.6m
9 Janet Evanovich £9m
10 Nicholas Sparks £8.5m
