Diana Athill, a British literary editor who worked with some of the finest writers of the 20th century — including Margaret Atwood, V.S. Naipaul and John Updike — before establishing herself as an award-winning memoirist of love, sex, childhood and aging, died Jan. 23 at a hospice in London. She was 101.

Her publicist, Pru Rowlandson of Granta, confirmed the death but did not give a precise cause.

Often described as the grande dame of British letters, Ms. Athill (pronounced AT-hill) spent much of her career as a literary midwife, working with writers to turn rough drafts into bound books. Raised in privilege on a Georgian estate in the Norfolk countryside, she worked at the BBC during World War II before helping her friend and former lover André Deutsch, a Hungarian emigrant, establish the independent publishing house that bore his name.

Originally known as Allan Wingate, the firm came to prominence in 1949 publishing Norman Mailer’s expletive-filled novel “The Naked and the Dead,” which rendered a certain four-letter word as “fug” and was briefly held up by a court injunction. Re-christened André Deutsch Ltd., the publishing house went on to release works by Brian Moore, Naipaul and Mordecai Richler before anyone else, and was the first British publisher of Atwood, Philip Roth and Updike.

Its editorial decisions were guided in large part by Ms. Athill, who was known for her deft touch with manuscripts and authors who also included Jack Kerouac, Molly Keane and Jean Rhys, who was struggling with alcoholism and debt when Ms. Athill helped her complete her 1966 masterpiece, “Wide Sargasso Sea.”

But her disciplined approach to editing was matched by an unconventional personal life, in which Ms. Athill maintained a slew of romantic relationships with married men and some of her own writers. Being “the other woman,” she said, “was what I was best at” — a state of being that offered her “love with all the plums and none of the pudding.”

Ms. Athill’s romantic life and celebrated editing career served as twin threads in her eight memoirs, works of unsentimental, crystalline prose that earned her a devoted audience in England in recent years, even as they shocked some readers who expected more demure material from a nonagenarian writer.

Romance, she wrote, had been at the center of her life since the age of 4, when she spied the brown-eyed “gardener’s ‘boy’ ” from a bathroom window and, in a childish effort to draw his attention, spat on his head. “He felt it, looked up, those beautiful brown eyes met mine — and I shot out of the lavatory, scarlet and breathless with excitement,” Ms. Athill later wrote. “After which I was never, so far as I can remember, out of love.”

Her first memoir, “Instead of a Letter” (1962), centered on her engagement to Tony Irvine, an Oxford student she met at age 15 when he was tutoring her younger brother. The two later became engaged, but after he was posted to Egypt as a pilot during World War II, Tony — dubbed “Paul” in the book — went two years without answering her letters. Eventually he told her he was marrying someone else, and he died when his plane crashed in Greece.

“My soul shrank to the size of a pea,” Ms. Athill wrote. For two decades, she said, she felt unworthy of love, devoid of joy even as her editing career took off. “If at any time during those 20 years someone had stopped me and said, ‘What is the truth about your life?,’ I would have said, ‘It’s a failure,’ ” she told the BBC radio program Desert Island Discs.

She bolstered her confidence by writing after work, following Rhys’s suggestion that writers had to be totally honest about their experiences. After a few short stories she completed “Instead of a Letter” in a rush that left her invigorated, even as it scandalized her button-down mother.

“The reader feels that what he is reading is as true a portrait of the writer and her experience as any words on paper can achieve,” journalist and literary editor Ian Jack later wrote in the Guardian. Ms. Athill, he added, “opened up what could have been a narrow story of injury and self-absorption into a book that takes pleasure in the world.”

Ms. Athill’s subsequent memoirs drew similar praise but generally attained only a cult following. That changed in her early 90s, when she received a National Book Critics Circle Award and a Costa Book Award, a literary honor for writers based in Britain and Ireland, for “Somewhere Towards the End” (2009).

A frank memoir of old age, it was a bestseller and made the elegant, white-haired Ms. Athill a literary star in Britain. The book was inspired by a realization that memoirs, including several of her own, tended to focus on youth; there were few books, she said, about growing old.

“There are no lessons to be learnt, no discoveries to be made, no solutions to offer,” she concluded. “I find myself left with nothing but a few random thoughts. One of them is that from up here I can look back and see that although a human life is less than the blink of an eyelid in terms of the universe, within its own framework it is amazingly capacious so that it can contain many opposites. One life can contain serenity and tumult, heartbreak and happiness, coldness and warmth, grabbing and giving — and also more particular opposites such as a neurotic conviction that one is a flop and a consciousness of success amounting to smugness.”

The oldest of five children, Diana Athill was born in London on Dec. 21, 1917, during a World War I Zeppelin raid. Her father served in the British army, and her mother was a homemaker who suffered a nervous breakdown after having an affair, Ms. Athill said.

Raised at Ditchingham Hall, her grandmother’s estate in Norfolk, she went on to receive a bachelor’s degree from the University of Oxford in 1939. She met Deutsch at a party after the war, and they worked together for nearly 50 years. The publishing company they built together is now an imprint of Carlton Publishing Group.

Ms. Athill’s other books included a novel and story collection, as well as two memoirs: “After a Funeral” (1986), about her friendship and onetime love affair with Egyptian writer Waguih Ghali, who committed suicide in her apartment in 1969; and “Make Believe: A True Story” (1993), about her relationship with African American writer Hakim Jamal, a disciple of Malcolm X who was slain in 1973.

After retiring from editing, she wrote “Stet: An Editor’s Life” (2000); “Yesterday Morning” (2002), a recollection of her childhood; and “Alive, Alive Oh!” (2015), which described a miscarriage that nearly killed her when she was 43, as well as her painful decision to move into an “old person’s home” at 91.

She never married, but spent four decades living with, and eventually caring for, Barry Reckord, a Jamaican playwright she often described as her “lodger.” He died in 2011. There are no immediate survivors.

“I have always been a watcher. Of myself in particular,” Ms. Athill told the Telegraph in 2011, reflecting on her career. “Even at times of acute unhappiness I’ve watched myself being unhappy. I also think I’m one of those people who has never been wholly involved in an emotion, but then I think a lot of writers are like that.”