On Tuesday night, a procession of writers, editors and publishing-industry veterans stepped past the lions outside the New York Public Library’s main branch on Fifth Avenue as they made their way to a dinner celebrating the acquisition of the archives of Joan Didion and John Gregory Dunne.

The vast collection, which the library bought in January for an undisclosed price, contains manuscripts, family photos, recipes and financial documents that provide a glimpse into Ms. Didion’s private life and creative process. At the time of her death at 87 in 2021, she was one of the nation’s most vaunted writers, and the archive contains everything from letters she wrote to her parents when she was a student at the University of California, Berkeley, to drafts of her books, including “The Year of Magical Thinking” and “Blue Nights.”

Combined with the papers of her husband, Mr. Dunne, who died at 71 in 2003, Ms. Didion’s will be made available to the public in two years. The collection will allow biographers an intimate look at one of the country’s most celebrated literary couples. Mr. Dunne, a noted journalist and novelist, was Ms. Didion’s closest collaborator, and the archive includes guest lists for their dinner parties, their edits of each other’s manuscripts and screenplay drafts of films they wrote together like “The Panic in Needle Park” and “Play It as It Lays.”

In a grand hall on the library’s third floor, guests mingled by cocktail tables decorated with framed recipes typed up by Ms. Didion for a melon salad with mint and cucumbers, “Mexican Chicken” and other dishes.

“She took entertaining seriously and was almost militaristic with her recipes,” said the archive’s acquiring curator, Julie Golia, as a waiter offered a tray of eggplant Parmesan snacks. “She was precise about how each recipe should be delivered. The conversations that must have happened at those dinner parties, you can only imagine.”

Under a glass display was more Didion ephemera — Christmas cards to the writer Tom Wolfe and her letters to editors she worked with, including Robert Silvers at The New York Review of Books and Henry Robbins at Farrar, Straus & Giroux.

“Sorry I took so long,” she wrote to Mr. Robbins in 1967, not long before the publication of her nonfiction collection “Slouching Towards Bethlehem.” “Part of the problem was that in re-reading the pieces I got mad all over again about those dropped clauses and missing commas. Also I read through a lot of stuff (not on this list) I could not could not could not stand and nobody to blame but myself.”

Soon, the guests sat at banquet tables, where they were served a kale salad inspired by one of Ms. Didion’s own preparations. From a stage, the actress Candice Bergen and her daughter, the Vogue writer Chloe Malle, read letters that Ms. Didion wrote to her parents after moving to New York from California in the 1950s.

In a letter read by Ms. Bergen, Ms. Didion recounted her romance with Manhattan, trying to conquer her shyness, watching teenage boys dive into the East River at night and her dates with a man named Jerry, whose marriage proposal she rejected because she considered him dull.

Many of those present had known Ms. Didion personally, but seemingly all of them listened with fascination: The letters revealed Ms. Didion when she was just another struggling writer, long before her authorial persona had become at least as famous as her work.

Part of Ms. Didion’s enduring appeal has to do with her chic image and the enigma that went with it — behind the sunglasses, beneath the myth, who was she? In an onstage conversation with the writer Sloane Crosley, Ms. Didion’s nephew, the actor, director and producer Griffin Dunne, suggested that the archive might satisfy that curiosity for younger fans.

“Now she’s a figure on tote bags, almost like a ubiquitous Che Guevara figure,” Mr. Dunne said. “But people, they always want to know what she was like, and that’s what these letters are. All those girls in the subway carrying Joan Didion books, now they’ll have a place to go find out.”

During the sit-down dinner, Mr. Dunne, who directed the 2017 Netflix documentary “Joan Didion: The Center Will Not Hold,” reflected further on the lore surrounding his aunt.

“Did she have self-awareness of it?” he said. “I think she understood what that photo of her standing in front of the Stingray was. With the cigarette and loose hair. She was conscious of where she fit into the culture. She made no secret of her ambition.”

Taking in the night over a plate of brick chicken served with brown-butter sauce was Calvin Trillin, a longtime staff writer for The New Yorker and a close friend of Ms. Didion’s.

“Despite all the stories about her as a kind of spirit, underneath that ethereal image, she had a very practical side,” Mr. Trillin said. He recalled how she had been the president of her Upper East Side co-op’s board and how she and her husband appreciated routine when it came to eating out, favoring old-guard restaurants like Elio’s.

At night’s end, the guests walked through the library’s empty halls, their chatter echoing as they headed into a warm spring night. One of them was Steven ​​M.L. Aronson, an author of the 2017 biography “Avedon: Something Personal,” who lived near Ms. Didion on the Upper East Side. As he hailed a cab on Fifth Avenue, he recalled accompanying her on walks with her wheaten terrier, Ellie, and his American water spaniel, Quintus.

He paused to consider whether the real Ms. Didion could be found in a heap of documents.

“I think it was probably all myth,” Mr. Aronson said. “She made her own legend and she lived it. But through someone’s papers and letters, you can see the process of how they created themselves.”