Mary Heilmann, who was in her 60s when she belatedly achieved wide acclaim for her ebulliently colored, loose-limbed, often lopsided abstract paintings, died on Friday night. She was 86.

Her death, at a hospital in Riverhead, N.Y., was confirmed by Liane Thatcher, her studio manager, who said the cause was complications from a fall a week ago.

Ms. Heilmann’s paintings, which poked fun at the geometric precision favored by her Minimalist colleagues, are easy to recognize. She was a master of the wobbly line, taking the rectilinear grid employed by artists from Piet Mondrian in the 1920s to Sol LeWitt in the ’60s, and skewing and destabilizing it. It was as if she sought to drain Modernism of its lofty concepts and utopian striving and lend it an offhand charm. Some of her most enchanting paintings look as if they if they were done by an artist who had misplaced her T-square and ruler.

Originally trained as a ceramist, Ms. Heilmann favored high-key colors that at times drip and run like glazes on the side of a pot. Her affection for hot pinks and oranges, with their intimations of teenage-girl taste, amounted to its own sly assault on virile dogmas of the past.

“Mary confronted all the macho nonsense of the time with cool confidence,” the artist Laura Owens, a former student of Ms. Heilmann’s, said in an interview. “At a time when painters took their own importance too seriously, Mary doubled down, paradoxically, on the casual gesture.”

Within the art world, Ms. Heilmann was an emblem of the professional obstacles faced by women artists of her generation. “I was such an underdog for so long,” she said without bitterness in an interview with The New York Times in 2008.

That was when her first museum retrospective, modestly titled “Mary Heilmann: To Be Someone,” was about to open at the New Museum in New York.

It had already appeared at the Orange County Museum of Art, in Newport Beach, Calif., and won high praise. At 67, Ms. Heilmann was recognized as a major influence on prominent artists including Ms. Owens, Jessica Stockholder and Elizabeth Peyton, all of whom had found something liberating in the deliberate, don’t-overthink-it lightness of her sensibility.

Ellsworth Kelly, the dean of American hard-edged abstract painting, said at the time, “I’ve always felt that Mary Heilmann is the best of the new abstractionists.”

Mary Ann Heilmann was born in San Francisco on Jan. 3, 1940, and grew up in a religiously observant Irish Catholic family. Her mother, the former Mary Florence Webb, was a nurse. Her father, John Sherman Heilmann, was a civil engineer who worked primarily on roads.

When she was 7, her father took a job building freeways and moved the family to El Segundo, a seaside village south of Los Angeles. They lived in a bungalow near the beach, and Ms. Heilmann later spoke of the thrill of tumbling down sand dunes and swimming in the ocean.

At 12, she began training as a competitive swimmer and diver, traveling on an hourlong bus ride to the Los Angeles Athletic Club every day after school. Less than a year later, all that ended abruptly when her father died of colon cancer and her mother moved the family back to San Francisco.

Ms. Heilmann attended college at the University of California, Santa Barbara, majoring in English literature. An early affection for tossing pots on the wheel led her to graduate school at the University of California, Berkeley, where she studied both ceramics and sculpture with Peter Voulkos, a well-known artist who believed in subjecting clay to Abstract Expressionist theatrics.

As Ms. Heilmann later recalled, Mr. Voulkos liked to walk across the classroom holding a homemade pot, then trip (or rather, as she said, “fake trip”), with the pot smashing on the floor. He would collect the broken shards and assemble them into a surprisingly interesting sculpture.

Ms. Heilmann’s own early sculptures, which consisted of ragged-looking objects constructed from inexpensive craft-shop materials like plastic clay, tin foil, cotton balls, bamboo and glitter, similarly sought to foreground the process of their making.

In 1968, after earning a master’s degree from Berkeley, she struck out for New York, intent on making a name for herself as a sculptor.

By then, Richard Serra, a friend of hers from high school, was living in Manhattan and gaining an underground reputation for “splash sculptures” he made from tossing molten lead. He took Ms. Heilmann to Max’s Kansas City, then a popular artists’ hangout. In the back room, in the hazy red light emitted by a Dan Flavin fluorescent tube, she befriended a circle that included Robert Smithson, John Duff and Carl Andre, sculptors who insisted that painting was dead.

Ms. Heilmann agreed with them. But in those days, female sculptors had great difficulty launching careers. Of the 22 artists in the Whitney Museum of American Art’s landmark 1969 exhibition “Anti-Illusion: Procedures/Materials,” 20 were male.

Ms. Heilmann was devastated when she was passed over for that exhibition and several other important group shows. Hoping to cut her losses, she abandoned sculpture and took up painting.

It seemed like a reckless decision. For one thing, she had no academic training in painting; for another, what sculptor worth her salt packs it all up at the age of 30? But she was pleased by the very contrariness of her act.

At the time she was supporting herself by teaching at the State University of New York at Stony Brook, and she credited her students — as well as much younger ones she had taught earlier — with furnishing her with ideas for paintings. For instance, in “Little 9 x 9” (1973), she added an off-kilter grid to a mostly red canvas by wiping away pigment with her fingers, a technique generally known as finger painting.

As her style evolved, it retained its aura of playful ease. In 1979, after joining the powerful Holly Solomon Gallery in SoHo, Ms. Heilmann exhibited a series of paintings of rectangles in pink and black, a color combination that was deliberately saccharine and reminiscent of nothing so much as Good & Plenty candy.

Critics didn’t know how to read these works. Ms. Heilmann was deeply hurt by a review that appeared in The Village Voice, perhaps because it was written by a female critic. Kay Larsen, bothered by the seeming lackadaisicalness of the pink-and-black paintings, concluded that they could use some “real muscle.”

Ms. Heilmann, she wrote, “hasn’t been doing her push-ups.”

In 1986, Ms. Heilmann rode her bicycle to Avenue B in the East Village to visit the relatively new Pat Hearn Gallery, “a powerful, radical painting gallery,” as she described it in her 1999 memoir, “The All Night Movie.”

With the help of her friend Ross Bleckner, who exhibited there, Ms. Heilmann joined the gallery. In the next decade, she gained an adoring following, especially among younger artists who were looking for an alternative to the excesses of the 1980s art scene, that cash-drunk era dominated by the portentous style of Neo-Expressionism.

In addition to paintings, Ms. Heilmann won acclaim for her boxy plywood chairs, which she started making in 2002. If they owed a debt to Donald Judd’s geometric furniture, they also offered a critique of his stripped-to-the-bone Minimalism.

“Judd’s chairs were not very comfortable, but mine are,” she told Vogue.

Indeed, her chairs generally have webbed seats and backs made from strips of polypropylene, not unlike classic aluminum lawn chairs.

Ms. Heilmann was delighted when 45 of her chairs — made for the occasion from weatherproofed marine plywood and painted in lollipop shades of lemon yellow and cherry red — were installed in 2015 on an outdoor terrace to help inaugurate the Whitney’s new building in the Meatpacking District.

A decade later, the chairs reappeared at the museum, inside this time, in a gallery overlooking the Hudson River. The exhibition was named “Long Line,” after a 2020 Heilmann painting that was dramatically enlarged and reproduced on the room’s walls, its alternating teal and white stripes evoking the ocean waves of her childhood. The show closed on Jan. 19.

Asked once how she came up with ideas for her paintings, she replied in her typically down-to-earth manner: “I mostly just think. A lot of it is daydreaming. A lot of it is sitting.”

Ms. Heilmann never married. She is survived by her nieces Ann Jaime and Christine Heilmann, and her nephew John Heilmann Jr.

She tended to describe her life as a solitary crusade for artistic accomplishment.

“I didn’t want to move to the suburbs and have a family and take care of the children, the husband and all that,” she said in a 1999 interview with Mr. Bleckner for Bomb magazine.

“It probably comes from my Catholic upbringing,” she added. In her youth, Ms. Heilmann said, she loved reading about the lives of saints, because “there was nobody in their story except them and God, and that was a model for me.”