Christopher Little, who as a struggling literary agent took a chance on a scrappy submission about tween-age wizards — even though he once disdained children’s fiction as a money-loser — and built it into the most successful literary empire in history on the strength of its lead character, Harry Potter, died on Jan. 7 at his home in London. He was 79.

His death, from cancer, was announced by his firm, the Christopher Little Literary Agency.

J.K. Rowling, the author of the Harry Potter series, was an unpublished, unemployed single mother in Edinburgh in 1995 when she sent Mr. Little the first three chapters of her first book after finding his name in a directory of literary agents. Knowing nothing about the business, she picked him because his name made him sound like a character from a children’s book.

Mr. Little submitted the manuscript for “Harry Potter and the Philosopher’s Stone” to 12 publishers. He received 12 rejections in response, before selling it for £2,500, or about $3,400 (the equivalent of about $5,800 today). It was a meager amount, but his genius was in the details: He sold only the rights to publish it in Britain and the Commonwealth, and he asked for high royalties.

It was the beginning of what one British newspaper called “the most commercially successful relationship in literary history.” The book was a hit in Britain, and Mr. Little sold the U.S. rights for just over $100,000 and, soon after that, the film rights for $1.8 million.

Mr. Little did more than launch Ms. Rowling’s career. He was the architect of the entertainment powerhouse that grew up around Harry Potter, helping line up everything from Legos to amusement parks.

Ms. Rowling was the first author to earn more than $1 billion off her work, and it’s no surprise that her agent did well too: By some estimates Mr. Little made over $60 million from the Harry Potter franchise. He never claimed credit for her success, but he was ever-present in the background, appearing alongside his client at book launches and movie premieres, enjoying those brief moments in the limelight.

The relationship was not to last. In 2011 Ms. Rowling abruptly split with Mr. Little, opting to follow his in-house lawyer, Neil Blair, who had left to establish his own agency. Mr. Little, shocked, threatened to sue, but he backed off after Ms. Rowling paid him an undisclosed sum.

“Christopher Little was the first person in the publishing industry to believe in me,” Ms. Rowling said in a statement after his death. “Being taken on by his agency was a huge break for an unknown writer. He represented me throughout the 10 years I published Harry Potter and, in doing so, changed my life.”

Christopher John Little was born on Oct. 10, 1941, in York, in northeastern England, and grew up in Liversedge, a small town between Manchester and Leeds. His father, Bernard, flew Spitfires for the Royal Air Force in the Battle of Britain during World War II and became an officer of the Order of the British Empire. He later became a coroner. His mother, Nancy (Pickersgill) Little, was a secretary.

Mr. Little’s first marriage, to Linda Frewen, ended in divorce. They had two sons, Nicholas and Kim, who survive him, as do two grandchildren and his second wife, Gilly, whom he married in 2012.

Mr. Little left school at 16 to work for his uncle’s textile firm. He later worked for another textile company in France, and from 1965 to 1974 lived in Hong Kong and other Asian cities. He sold office supplies, worsted wool cloth and, eventually, mutual funds, developing a reputation as a steely negotiator. After returning to England, he opened a recruiting firm.

In 1979 Philip Nicholson, a childhood friend who had also lived in Hong Kong and knew something of Mr. Little’s deal-making skills, asked him to help sell his first novel, a thriller he had written under the pen name A.J. Quinnell. The book, “Man on Fire,” went on to sell 7.5 million copies and was twice adapted for film, most recently in 2004, with Denzel Washington in the lead.

Flush with his early success, Mr. Little opened the Christopher Little Literary Agency, though he maintained that selling manuscripts was just a “hobby.” It soon became more than that — in 1992, with a stable of about 20 writers, he shut down his recruiting business.

But he struggled to replicate that first win. His office near Victoria Station, in central London, was cramped with towering piles of manuscripts. One of his writers called it “near-Dickensian.”

Mr. Little, who preferred to pursue thrillers and romance novels, initially dismissed Ms. Rowling’s submission, throwing it away without reading it. But its elaborate binding caught the eye of his office manager, Bryony Evens, who read it and, intrigued, insisted he give it a chance. Like her, he was immediately taken with the tale of wizards and muggles, of Dumbledore and Hermione and He Who Must Not Be Named.

An intensely private man, Mr. Little rarely gave interviews. But in a conversation with The Sunday Telegraph in 2003, he said, “I thought that there was something really special there, although we could never have guessed what would happen to it.”

Without the money to print the usual 10 copies that publishers expected with each submission, he had Ms. Evens retrieve the manuscripts after they were rejected, so he could send them back out.

He finally persuaded Bloomsbury to take on the book, helped along by the young daughter of its publisher, who loved it. The initial print run was just 500 copies. But Mr. Little refused to push further, for foreign or film rights; by this point, he knew it would be a success, and he wanted the hype to build before negotiating.

“We had to wait two years, but it worked. We got the reviews and the word of mouth,” he told The Telegraph. “We just sat back and waited for the offers to come in.”

A stocky 6-foot-4, with immense feathery eyebrows, Mr. Little tacked easily between warmly avuncular and quietly menacing, a quality he leaned on heavily while building the Harry Potter franchise.

He laid the groundwork for the intricate deals that led, for instance, to not one but two Harry Potter-themed sections at the Universal Studios theme parks in Florida. And he aggressively pursued anyone who tried to use the brand without permission: He once blocked a short play, performed for charity, that had dared to feature characters from the book.

Critical to that legal vigilance was Mr. Blair, his agency’s in-house counsel. It was Mr. Blair who championed Pottermore, an online portal for all things Potter. (It is now known as Wizarding World.) He and Ms. Rowling left the agency just days before Pottermore went live — and days before the premiere of “Harry Potter and the Deathly Hallows: Part 2,” the last film in the series.

Though friends said the loss of Ms. Rowling as a client remained a sore spot for Mr. Little, he continued to flourish, representing best-selling authors like Darren O’Shaughnessy and Janet Gleeson. In 2012 he merged his agency with Curtis Brown, a much larger British firm, and continued to take on new clients — including unpublished writers as new to the business as Ms. Rowling had once been.

One of those authors, brought on while he still represented Ms. Rowling, was Shiromi Pinto, the author most recently of the novel “Plastic Emotions.”

“It was because he took a chance with her,” Ms. Pinto said, “that he was able to take a chance on someone like me.”