The American poet and writer Maggie Smith exudes a beatific warmth, so it seemed apt — a felicitous pairing of author and venue — that her recent book tour included an evening at a Brooklyn church. The pews were crowded with admirers, many feverishly reading her new memoir even as they waited for her to speak.

The book, “You Could Make This Place Beautiful,” is about the collapse of Ms. Smith’s marriage — from her discovery of her husband’s affair to his decision to walk out — and how writing helped her survive it. Alert readers will recognize the title as a line from her viral 2016 poem “Good Bones,” which became a social-media hit and then a wider cultural phenomenon, a “mantra of hope in hard times,” as Slate put it.

“You Could Make This Place Beautiful,” which just made its debut on The New York Times’s best-seller list in the No. 3 position for hardcover nonfiction, is actually the second book Ms. Smith has written about her divorce. (The first was “Keep Moving,” released in 2020.) Somehow between the publication of “Good Bones” and now, Ms. Smith became that most surprising of things, a celebrity poet.

But if she has been a beneficiary of her success, so she has also been a victim of it. As she says in the book: “My marriage was never the same after that poem.”

At the church, where Ms. Smith — wearing a black-and-white dress and a pair of pink heels — was appearing in conversation with the novelist Leslie Jamison, the audience Q. and A. was pervaded by fan-girl giddiness. (“I love your dress,” one question began.) There were several queries about Ms. Smith’s writing process, and one about her former husband, an unnamed lawyer who wafts unpleasantly through her book, both villain and cipher.

“Did you have the impulse to ask anybody for permission,” one woman asked, “and were you concerned with how your ex-husband would feel?”

Ms. Smith flashed a serene smile. “I so respect and appreciate that question, and um, no, I did not feel the need to ask anyone for permission,” she said. She added: “I can’t make decisions in my life based on fear.”

In the book she describes how, soon after her husband left the house he shared with her and their two children, she emailed him a draft of an essay she’d written about their breakup for the Times’s “Modern Love” column. He responded, she says, with a bossy litany of proposed changes — tiny correctives to details — designed to cast him in a better light. Told by her editor that the changes would “weaken” the piece, she rejected most of them.

This time around, she said, she had no interest in soliciting feedback, suggestions or permission of any kind from her former husband. She didn’t even tell him about the book in advance.

“If you want someone not to ask you for input on their writing,” she said in an interview, speaking of her ex, “providing edits like that is a good way to do it.”

Ms. Smith was chatting in the empty lobby of her hotel in Brooklyn the day before the church event. She is as frank, friendly and accommodating in conversation as she is in her work. But despite her apparent openness, there is a vein of steel in her, a sense that, having thoroughly examined her experience from every angle in the book, she does not want to be second-guessed.

“Keep Moving,” Ms. Smith’s last book, interspersed short essays with inspirational advice and affirmation in Twitter-size morsels. (Indeed, many of them first appeared on Twitter.) Sample morsel: “Write breathe on your to-do list. Write blink. Write sit and eat. Then cross everything off. How satisfying! Give yourself credit for living. KEEP MOVING.”

The book was received as a cry of hope for a depressed world full of people who, like Ms. Smith, were facing personal crises in the midst of a global catastrophe. It had a special resonance for women juggling work, home, children and partners from their bedrooms in lockdown. Glennon Doyle, another writer who has gained a huge following by parlaying the vicissitudes of her personal life into multiple best-selling memoirs, enthusiastically blurbed the book. (She said that it is a reminder that “you that you can feel and survive deep loss, sink into life’s deep beauty, and constantly, constantly make yourself new.”)

Ms. Smith understands the irony of her situation, of course: that the debacle at home provided material for the book, which in turn gave her new financial security to support herself. The material also gave her the impetus — and the audience — to write a second book. As one friend commented on Instagram when Ms. Smith announced plans to publish “Keep Moving”: “You took those lemons and made lemonade, and then you added MF vodka to it.”

Yes, Ms. Smith says in “You Could Make This Place Beautiful” — but.

“I’m trying to tell you the truth, so let me be clear: I didn’t want this lemonade,” she writes. “My kids didn’t want this lemonade. The lemonade was not worth the lemons. And yet, the lemons were mine. I had to make something from them, so I did. I wrote.”

At the church, audience members talked about the rawness and honesty of Ms. Smith’s work, how it feels as if she is speaking directly to them.

“There’s something so comforting and familiar about sitting down with her writing,” said Brianna Avenia-Tapper, 41, an editor and writer who is at work on her own memoir, which she describes as being about “birth, control and birth control.” She added: “It’s sort of a thing right now, to be writing about divorce, and I love the sense of welcome and warmth she brings to it.”

“Keep Moving” was Ms. Smith’s fourth book, after three books of poems. She had won numerous writing awards before, and her poems had been widely published in journals and magazines, including The New Yorker and The Paris Review. But with “Keep Moving,” she invited the world to peer into her home and her psyche.

“Is it unnerving at times to write something deeply personal?” she said in the interview. “Yes, because whenever you write anything you’re sending it off like a message in a bottle. The more people I send it off to the more chance there is that it will be misconstrued or judged.”

Ms. Smith called it an “honor” to be more widely read. But it has brought the added pressure of attention in real time.

“I was able to write my first three books without having a sense of reader expectations,” she said. “But how do I go on doing this and pretend no one’s watching?”

Ms. Smith addresses this in the memoir, which is less a linear narrative than a series of musings — some short essays, some chapters as brief as a line — and a meta-dissection of the act of writing about something so raw and wrenching. It is also an excavation, a murder inquiry, an attempt to answer questions that themselves are hard to articulate. What happened? Why did it happen? Was there a single cause? Is there a way to make peace with the unknown? How should you tell a story this convoluted? She circles back to these questions again and again.

As outlined in the book, the fault lines in her marriage were familiar, especially the gender dynamics: She mostly tended the house and the kids, writing at home in her spare (“spare”) time, while her husband mostly made the money that paid the bills, benefiting from a status quo in which she took care of the details that provided the scaffolding for their home life.

But when “Good Bones” became unexpectedly famous — when its second half was read aloud by a character on the television show “Madam Secretary,” when Meryl Streep recited it at a poetry gala at Lincoln Center, when it inundated Twitter and Instagram feeds and was crowned “the official poem of 2016” — the demands on its author multiplied. Suddenly, Ms. Smith wasn’t just a mother and wife who wrote poems when she had a free moment. She found herself invited to readings, conferences and seminars; her husband had to pick up the slack.

Her husband, she says, was not pleased.

“When I would call home from a trip, I remember feeling like I was in trouble,” she writes. “I’d made his life more difficult, and I might pay for that with the silent treatment or a cold reception when I returned home.”

Ms. Smith is comfortable making herself her own subject and said she rejected the idea of fictionalizing her divorce in the way of, say, Nora Ephron, who skewered her ex-husband, Carl Bernstein, in her novel “Heartburn.”

“That wouldn’t have addressed part of my purpose, which was to understand my experience,” Ms. Smith said. She says she was inspired, in part, by the writing of people like Deborah Levy and Rachel Cusk, though with elements of experimentation in her form. “There’s a whole genre of the divorce memoir and at the same time I didn’t want this to be just that,” she said.

Ms. Smith said she was dating again and was happy, though she didn’t want to go into the details. She added that she would never fully understand what happened in her marriage, in large part because she says her husband (who declined a request to be interviewed for this article) never fully explained why he cheated and why he left. That is the fundamental mystery at the heart of “You Could Make This Place Beautiful.”

One thing is clear to her, though. “My writing was not the problem,” she said. “It was the solution.”