Correction: This story has been revised to reflect updated information provided by Dr. Rowley’s family about the cause of her death. A previous version of the story cited Australian news reports that attributed Dr. Rowley’s death to a series of strokes and heart attacks.

Hazel Rowley, an acclaimed biographer of wide-ranging subjects — from “Native Son” author Richard Wright to French existentialist Jean-Paul Sartre — and whose last published book explored the complicated marriage of Franklin and Eleanor Roose­velt, died March 1 at a hospital in New York. She was 59.

The cause was complications from multiple strokes that were caused by a bacterial infection, according to Della Rowley, Dr. Rowley’s sister.

Dr. Rowley held a doctorate in French studies but left the academy to write for a general audience. Born in England, she spent most of her life abroad in Australia and the United States.

She said she was drawn to writing about outsiders, and she found perhaps her widest audience by examining unconventional love lives. In 2005, she won international attention for her account of the relationship between Sartre and the feminist writer and philosopher Simone de Beauvoir. In “Tete-a-Tete: Simone de Beauvoir and Jean-Paul Sartre,”Dr. Rowley drew from unpublished letters, journals and personal interviews to create an unsentimental portrait of the couple and their romantic entanglements and jealousies.

“The result is an enthralling book, almost a highbrow Francophile edition of US Weekly,” wrote Washington Post book critic Michael Dirda. “But instead of Brad and Jen and Angelina, here we find an ugly, walleyed existentialist philosopher, the elegantly beautiful author of ‘The Second Sex’ and the Gallic equivalent of a bevy of young starlets who share the bed of one or the other — or sometimes both. Readers will turn these pages alternately mesmerized and appalled.”

In “Franklin and Eleanor” (2010), Dr. Rowley again shed light on the intricacies of a famous relationship.

Dr. Rowley argued that, contrary to popular understanding, the Roosevelts’ marriage did not all but end after revelations of Franklin’s affair with Eleanor’s secretary. Instead, the couple shaped an un­or­tho­dox yet strong partnership that endured political ambition and illness to become what the author described as “one of the most interesting and radical marriages in history.”

In a 2007 essay, Dr. Rowley compared writing biographies to being in love. “Much energy and empathy goes into putting yourself into someone else’s shoes; you inevitably become obsessed,” she wrote.

“Finally, I finish the book. Do I feel relieved? No, I feel lost. It’s the end of an affair.”

Hazel Joan Rowley was born Nov. 16, 1951, in London and moved when she was young to Australia, where her father had taken a medical professorship.

As schoolgirls, she and a friend spent a summer vacation writing a novel. As a teenager, Hazel penned countless short stories and sent each off to potential publishers.

“They were all rejected, but even the rejection slips made me feel proud,” she once wrote. “Real writers get rejection slips.”

Dr. Rowley received bachelor’s and doctoral degrees from Australia’s Adelaide University and then taught at Deakin University in Melbourne. Besides her sister, survivors include her mother, Betty, and a brother, Martin.

She earned glowing reviews in 1994 for her first book, “Christina Stead,” a biography of the Australian novelist whose most famous work was “The Man Who Loved Children” (1940), about a dysfunctional family headed by a man modeled on Stead’s own father.

Stead led a wandering life, writing from Paris, civil war-torn Spain and New York, where she lived with her lover, the novelist and Marxist economist William Blake. She burned most of her papers before her death in 1983, making Dr. Rowley’s task daunting.

Dr. Rowley explored American race relations in her second book, a 2001 biography of the African American writer Richard Wright.

Terrified that she could not do justice to the story of a black man in America, Dr. Rowley had initially turned down her publisher’s advance on the Wright book. A friend and fellow writer urged her to reconsider.

“In the next few weeks, the figure of Richard Wright loomed before me,” Dr. Rowley wrote. “His whole life was about courage, daring and determination. He always grappled with the sense that he was an interloper in a territory meant only for whites. He hadn’t given in, had he?”

Dr. Rowley left her teaching position at Deakin and moved to the United States to research Wright’s life.

A visiting fellow at the W.E.B. Du Bois Institute at Harvard University, she arrived in the country with a three-year visa but easily received a green card, she wrote, “in a category the name of which I relish: ‘Alien of exceptional ability.’ ”