Asking himself “Why I write”, George Orwell gave four reasons: aesthetic enthusiasm, historical impulse, political purpose and sheer egoism. Asked the same question ahead of a literary conference in Mexico City, Miriam Toews mentions the teenage letters she sent from Europe to her sister Marjorie (Marj or M as she calls her) as the reason she became a writer. Sorry, that won’t do for an answer, she’s told. Try again.

In a frenetic household set-up in Toronto, keeping an eye on her mother one moment, entertaining her grandchildren the next and warding off angry neighbours in between, she struggles to get her act together and makes a to-do list: “Wind Museum. Deranged skunk. North-west quadrant with ex. Conversación in Mexico City.” The skunk has distemper and keeps getting trapped in the window well. The Wind Museum is the collection she’d love to create, commemorating winds from all over the world (Harmattan, Calima, Mistral, Sirocco etc), if she can find a way to exhibit them. The ex is the father of her second child, who despite years of separation is still taking the royalties on her work – it’s time to meet him and end that arrangement.

Most pressing, though, is the Mexico City business. Since early childhood she has been “afflicted” with a need to write things down: “the fingers in my mind would begin typing”, and she’d carry on all day, touch-typing in her head, “as though that were the only way of proving to myself that I was alive, that what I was experiencing was real”. That could be an answer of sorts. Too late, though: she’s disinvited from the conference; the word CANCELLED appears across her photo in the programme.

A hopeless failure, then. But this book is a triumph – a meditation on writing, suicide, guilt and silence; a fragmented account of her life so far; and an illustration of why she’s one of Canada’s most admired writers (there’s now a plaque outside her former home in Steinbach, Manitoba, where she grew up as part of a Mennonite community). Though the Mexico City organiser missed the point, those letters to her sister were indeed her prime reason for writing. “Why do I write? Because she asked me to.” That was the deal they made. “You live. And I’ll write.”

Marj suffered from depression and in 2010 she killed herself, 12 years after their father Melvin had done the same. Toews wrote about Melvin, in his voice, in her book Swing Low (2000) and her relationship with Marj formed the basis for her novel All My Puny Sorrows (2014). Most of her work until now has been loosely autofictional. This time there are no disguises. She tells it as it is.

“You people (meaning, my family) don’t talk about your pain,” Toews’s partner tells her, “you just kill yourselves.” Toews herself came close to doing so one day while walking by the river Assiniboine, in Winnipeg, but rather than throwing herself in the water she threw her mobile phone instead. “A parable of perfect silence,” she calls it, but it’s her sister’s silence that preoccupies her – all those years before she died when she didn’t speak. “Was my sister’s silence an attempt to translate something that couldn’t be said? Something that would cause too much pain if it were to be said?’ The questions keep coming, with Toews disinclined to present writing (“this strange non-thing”) as any more creative or worthwhile than her sister’s wordlessness: “If silence says more, why write?”

As a hymn to their intimacy, maybe the writing did help keep her sister alive. The letters she sent from Europe, which come in a brilliant run of 30 pages late on in the book, date back to 1982, when Toews was travelling with her boyfriend Wolfie. The two of them are hard up and she’s increasingly disenchanted with him, not least when he busks with a penny whistle in Covent Garden (no, she won’t hold out a beret for coins) or queues to get a book signed by John Fowles when they haven’t the money for food. In Oxford she lies on the grass, unaware there’s a cricket match going on. In Paris they’re chased out of a park by guards with whistles. In Rouen their bikes are stolen. In Corfu they’re pelted with pomegranates by a gang of children. They fall out, make up by having outdoor sex (“I still have tiny pieces of rock ground heroically into my back and ass”), fall out again. It’s hilarious. And she’s only 18. “Do you think I’ll soon be enjoying liquid lunches at the Algonquin Round Table, hahahaha.”

The hahahaha principle defines Toews. “Between you and me, I want to be a clown. I think I am a clown,” she tells Marj. It’s an inherited trait perhaps. Despite the sadness and depression, there’s a lot of laughter in the family, including an episode when they take a boat out to an uninhabited island, disembark for a picnic and return to find the boat has disappeared – rather than wail they all begin to laugh (later, miraculously, the boat drifts back to shore). Toews’s mother, a Scrabble genius, remains indomitably cheerful despite her losses, and is arguably the heroine of the book.

“Narrative as something dirty, to be avoided – I understand this,” Toews writes, and she does avoid it, up to a point, bobbing about in time and place, riffing on the Wind Museum, recounting how she refused to marry the father of her son and broke up with the father of her daughter. The awful and the laughable overlap. Her sister is attacked by a carful of young men and drenched in rancid brown liquid. Their mother is kidnapped and robbed. Their father doesn’t speak for a year. It might sink a less buoyant spirit but Toews makes comedy out of the chaos.

She does the same when she talks about her writing career. On a cruise with her mother, the pages of her manuscript are blown from the floor of her cabin into the sea. Her very first reading in another city is cancelled when the poet in charge runs off with her lover – Toews is left to sleep for three nights on a blow-up mattress in a garden shed. Her very existence is farcical: she was conceived on the night of her grandfather’s funeral, in a marital effort to ward off morbidity.

Why were her father and sister so silent, she asks her mother. “That’s easy, she replies, it was something they could control.” For Toews, writing serves the same purpose. She’s wired, anxious, on an adrenalin high and prone to panic attacks, “crazy with grief, guilt and dread”. Having to write dismays her. She’d love to stop obsessing about word order and become “a benign but wise grandmother, with a soft lap”. Then again, from what we see of her with her grandchildren, she is that anyway. Meanwhile, writing absorbs her sorrow and rage.

“Are you OK? I mean, you know, OK? I miss you so much,” Toews writes to her sister. “I wish I could take your sadness away.” She’s still trying, all these years later, closing with a 2023 letter to Marj (“You’ll like this”) about a stranger arriving at a Christmas Eve family gathering and being made welcome, though it turns out he has not been invited. There’s Toews for you. Her work’s so intimate you worry you’re intruding, but it’s fine, she welcomes you in.

A Truce That Is Not Peace by Miriam Toews is published by 4th Estate (£16.99). To support the Guardian order your copy at guardianbookshop.com. Delivery charges may apply.