Millicent Dillon, a novelist and prizewinning short-story writer who was best known for nonfiction that chronicled the eccentric, expatriate American literary couple Jane and Paul Bowles, died on Monday in Daly City, Calif. She was 99.

Her death, in a memory-care facility, was confirmed by the writer Wendy Lesser, her daughter.

Ms. Dillon trained as a physicist and worked at the Oak Ridge National Laboratory in Tennessee after World War II before she turned to writing after. Disturbed by the dropping of the atomic bomb on Hiroshima, she told an interviewer for the blog The Awl in 2016, “By the end of the war I knew I had to search elsewhere for my work in life.”

Ms. Dillon won the coveted O. Henry Award five times for her stories, but she devoted most of her writing career to the Bowleses — especially Jane, the neglected wife of the much better known Paul, whose 1949 novel, “The Sheltering Sky,” is widely regarded as a classic. “The Sheltering Sky” is set in North Africa, where the Bowleses lived for decades, mainly in Tangier, Morocco.

Ms. Dillon’s efforts enhanced the status of Jane Bowles as a “literary cult figure,” as the critic Susan Jacoby described her in assessing Ms. Dillon’s “A Little Original Sin: The Life and Work of Jane Bowles” in The New York Times Book Review in 1981.

“A Little Original Sin” marked the beginning of a sustained project by Ms. Dillon to bring Jane Bowles’s small but significant literary output into the public eye. Over the next two decades, she would edit “Out in the World: Selected Letters of Jane Bowles, 1935-1970” (1985), “The Portable Paul and Jane Bowles” (1994) and, for the Library of America, “Jane Bowles: Collected Writings” (2017). She also wrote the biography “You Are Not I: A Portrait of Paul Bowles” (1998).

Ms. Dillon’s focus on Jane Bowles reflected an unusual level of devotion to a writer who had produced only one novel, one full-length play and a handful of stories, “all of which read like promising first drafts,” as the critic Donna Rifkind wrote in The Times Literary Supplement in 1988.

That novel, “Two Serious Ladies,” published in 1943, before Ms. Bowles turned 30, chronicled the tumultuous misadventures, sexual and otherwise, of two bourgeois women, mirroring the constant emotional turmoil, heavy drinking and numerous lovers, mostly women, of the author’s own foreshortened life. (Paul Bowles was bisexual, and the couple had an open marriage.)

Ms. Dillon said she felt a unique bond with Jane Bowles, who died in 1973 at 56.

“From her first words something about what she told, something about what she withheld, her unique style and language, moved me deeply,” she recalled in an interview with the Library of America in 2017. She added: “The notion of time in the work has as much to do with the evasion of time as with time passing. Even as her characters talk about food and plain pleasures, they are obsessed with thoughts of sin and salvation.” (Gore Vidal once wrote of Jane Bowles, “She thought and talked a good deal about food and made powerful scenes in restaurants.”)

Ms. Dillon’s biography is an unusual interweaving of her own life with that of Ms. Bowles. In a prologue, she wrote about a series of coincidences that tied her to her subject. Ms. Bowles broke her right leg in 1931, Ms. Dillon wrote, and “I broke mine the same year.”

Commenting on Ms. Dillon’s biography in The London Review of Books in 2013, Lidija Haas criticized “the temptation to romanticize or over-identify with Bowles,” noting that the author “names the many Bowles acquaintances she encountered in her research who remarked on ‘how much I looked like Jane.’”

In her review in The Times Literary Supplement, Ms. Rifkind was also critical: “Dillon,” she wrote, “has traded certain standard requirements of biography — a coherent narrative, an intellectual curiosity which penetrates beyond the mere facts of a person’s life — for a drifting prose technique. The book is a potpourri, a compendium of information with no structure to contain it.”

Nonetheless, writing in The New Yorker in 2014, Negar Azimi, a senior editor of Bidoun, an arts and culture magazine about the Middle East, called Ms. Dillon’s biography “essential” for understanding Jane Bowles.

Ms. Dillon followed the same technique in her book about Paul Bowles, who was a composer as well as an author, interspersing accounts of her meetings with him in Tangier with facts about his life. “Why indeed had he gotten sick the very day of my arrival?” she asked in relating the outset of these encounters.

Ms. Dillon’s involvement with the Bowleses came after years in which she had concentrated on her own fiction, including the novels “The One in the Back Is Medea” (1973), “The Dance of the Mothers” (1991), “A Version of Love” (2003) and “Harry Gold” (2000), about a real-life spy, in which “Dillon the biographer inserts herself into the novel as a first-person narrator,” Elena Lappin wrote in The Times Book Review. She also wrote numerous stories, some of which were published in The Threepenny Review, a journal edited by her daughter Ms. Lesser.

Millicent Gerson was born in New York City on May 24, 1925, one of five children of Claire Gerson, a nurse, and Ephraim Gerson, who Ms. Lesser said abandoned the family when Ms. Dillon was a teenager.

Millicent attended Hunter College High School in Manhattan and received a degree in physics from Hunter College in 1944. She worked as a junior physicist on a government project at Princeton University from 1944 to 1945, was an assistant physicist at Oak Ridge in 1947, and became a staff writer for the Association of Scientists for Atomic Education in New York in 1948.

“Physics itself gave me great satisfaction because of the accuracy of the answers that told me how and why things in the physical world behaved as they did,” she told The Awl in 2016, but the news of Hiroshima “stunned” her.

She later enrolled in the creative writing program at San Francisco State University and, after receiving a master’s degree in 1966, taught creative writing at Foothill College in Los Altos Hills, Calif. She was an academic writer for Stanford University’s news and publications office from 1974 to 1983, the year she embarked on a full-time writing career.

In addition to Ms. Lesser, she is survived by another daughter, Janna Lesser; three grandchildren; and one great-grandchild. Her marriages to Murray Lesser and David Dillon ended in divorce.

In her interview with the Library of America, Ms. Dillon recalled returning to Jane Bowles’s work after an interval of some years and being reminded of what had enthralled her to begin with.

“I was stunned,” she said, “as I had been in my first reading, by the originality and emotional power of her work. In my rereading I came upon passages where there would be an unexpected turn in thought that would make me laugh out loud. Once again I was reminded of the remarkable alternation in her work between the ludicrous and the mystical.”

Alain Delaquérière contributed research.