Pat Kavanagh, a British literary agent whose hauteur, business acumen and abiding aura of mystery kept her distinguished string of writers and publishers fascinated, died Monday at her home in London. She was 68. The cause was a brain tumor, said a spokesman for United Agents, the literary agency where she worked.

For nearly 40 years, Kavanagh played a leading role in the London literary world, in part because of her marriage to the novelist Julian Barnes, more pertinently because of a client roster that included Ruth Rendell, William Trevor and Joanna Trollope, and not least by virtue of her personal style.

“She was glamorous, gorgeous and brilliant, but cutting if she thought you were less than the best,” said Robert Weil, the executive editor of W.W. Norton.

“She didn’t make it easy,” said Zoe Pagnamenta, a British agent in New York who has worked with many of Kavanagh’s writers. “You had to earn her respect and trust and friendship, which, when you did, made it all the more valuable.”

Intensely private, and no fan of the lunches and parties that most agents regard as happy hunting grounds, she found herself in the spotlight in 1995, when one of her most celebrated clients, Martin Amis, left her for the rival agent Andrew Wylie in pursuit of a mammoth advance for his novel “The Information.” The ensuing row was a feast for the British press.

Start on the stage

Patricia Olive Kavanagh was born in Durban, South Africa, where her father was a journalist. She studied at the University of Cape Town but set her sights on becoming an actress and performed briefly with a touring company. After arriving in Britain in 1964, she did appear in an uncredited, nonspeaking role in the film version of Dylan Thomas’ “Under Milk Wood,” but this turned out to be the high point of a noncareer that she had already abandoned.

While working as a copywriter for the J. Walter Thompson advertising agency, she answered an ad offering employment as a literary agent and found herself in the presence of A.D. Peters, a legendary agent who showed her the ropes. It was Peters, she said, who taught her the value of silence as a negotiating tool, and put her to work selling serial and newspaper rights for authors in the company’s illustrious stable. Her early clients included Arthur Koestler, Rebecca West, Tom Wolfe and S.J. Perelman.

She developed a reputation for good taste, sound judgment, few words and careful management of her clients, as well as a stylishly intimidating manner.

Tough love

“She was never one to undersell anything, and she was always on your case, but there was always the velvet glove,” said Sonny Mehta, the chairman and chief executive of Alfred A. Knopf.

She could be as tough with her authors as she was with publishers, refusing to varnish harsh truths or indulge writerly fantasies that ignored the economics of the business. At her death, her clients included Clive James, Margaret Drabble, Robert Harris and the British poet Andrew Motion.

Behind the patrician cheekbones and the formidable reserve lurked a wicked sense of humor. “I would sometimes fax her a New Yorker cartoon I thought would amuse her,” Pagnamenta said. “She would e-mail back, saying, ‘Very droll, Zoe. Hollow laugh ensues.’”

Wit was not the only surprise up her sleeve. In the 1980s, she left Barnes to embark on an affair with Jeanette Winterson, the author of “Oranges Are Not the Only Fruit.” She later returned to her husband, who survives her. The affair was fictionalized by Winterson in the novel “Written on the Body” (1992).