Roberta A. Kaplan, the celebrated lawyer who took on former President Donald J. Trump, and helped win marriage equality for gay Americans, is stepping down from the law firm she founded after clashing with her partners over her treatment of colleagues.

Ms. Kaplan, a hard-charging civil rights lawyer, announced that she was leaving the firm, Kaplan Hecker & Fink, which she formed in 2017, to start a new one.

Her departure followed months of internal frustration over Ms. Kaplan’s conduct toward other lawyers, according to people familiar with the matter. Those concerns led her colleagues to remove her from the firm’s management committee and precipitated her departure.

Ms. Kaplan’s former firm will be renamed Hecker Fink effective Monday. “Robbie brought us together and for that we owe her a debt of gratitude,” the firm’s remaining partners said in an internal memo reviewed by The New York Times.

“It was Robbie’s decision to leave the firm,” the firm’s two named partners, Julie Fink and Sean Hecker, said in a statement. “We wish her the very best and look forward to working with her and her new firm in the future.”

Ms. Kaplan’s lawyers had no immediate comment. Ms. Kaplan said in an interview with Bloomberg that she was leaving with a colleague because Kaplan Hecker & Fink had grown “in size and complexity beyond what I had in mind and I wanted to get back to something nimbler.”

Her departure was announced after The Times informed her personal lawyers that it was preparing to publish an article about Ms. Kaplan that would shine a light on complaints about what some employees said was an unprofessional office culture that she presided over.

The news that Ms. Kaplan was leaving her firm ricocheted through the legal community on Wednesday, with lawyers trying to figure out the circumstances behind the abrupt exit of one of the country’s most prominent attorneys.

Ms. Kaplan and her wife are deeply connected to the Democratic Party and she has been a heroic figure to many liberal activists. In addition to litigating the Supreme Court case that laid the groundwork for the national legalization of gay marriage, she became a leader of the #MeToo movement.

Most recently, she represented the writer E. Jean Carroll when she sued Mr. Trump for defamation, resulting in a landmark $83 million verdict against him this year.

When Ms. Kaplan, 57, left the white-shoe corporate law firm of Paul, Weiss to start her own boutique, she recruited lawyers with the promise of a different type of high-end firm — one driven by a progressive mission and free of the macho culture that is typical in the industry. She has said Kaplan Hecker & Fink was founded “on the principle that there always must be someone to stand up to a bully.”

By many measures, Ms. Kaplan’s firm was thriving. Its 60 or so lawyers in New York and Washington were winning big cases and prestigious prizes while pulling in paydays that rivaled those at much larger and older law firms.

When the #MeToo movement erupted, months after her firm opened its doors in a restored barn in the Hamptons, Ms. Kaplan quickly made it a signature issue.

Within weeks, she announced that she was representing a woman who was being sued by the film director Brett Ratner for defamation in one of the first legal battles of the #MeToo era. She publicly opined that lawyers like her had to “help facilitate women speaking up and speaking out on every front.”

Ms. Kaplan eventually became the chairwoman of Time’s Up, the celebrity-studded nonprofit that fought sexual harassment in the workplace, and co-founded its legal defense fund. She lobbied for legal changes that would make it easier for survivors to sue their assailants.

Even as she and her firm piled up victories, however, some employees were chafing under Ms. Kaplan’s leadership. Several people whom she worked with told The Times that she had insulted employees, inappropriately commented on their looks and threatened to derail people’s careers.

Lawyers for Ms. Kaplan denied that she made inappropriate comments to her colleagues and said her firm took allegations of workplace misconduct seriously. They added that “there is nothing more unremarkable than trial lawyers using colorful language, criticizing their peers and representing diverse clients with no expectation of ideological purity.”

In addition to the complaints about Ms. Kaplan’s treatment of colleagues, some lawyers at the firm were upset that some of her legal work seemed to conflict with the liberal ideals that Ms. Kaplan espoused.

In 2020, when Andrew M. Cuomo, then the governor of New York, faced allegations of sexual harassment, he turned to Ms. Kaplan for advice on how to confront the crisis. Ms. Kaplan’s role became public months later when the state attorney general released a report detailing the investigation of Mr. Cuomo’s actions.

The backlash was intense. More than 150 victims and victims advocates signed an open letter to the Time’s Up board, accusing it of prioritizing “its proximity to power over mission.” Ms. Kaplan soon resigned as chairwoman of the board.

One person familiar with the law firm’s internal dynamics said that the tensions over Ms. Kaplan began around that time, though they gathered force in recent months.

Ms. Kaplan tried to persuade some of her colleagues to leave with her, according to two people familiar with the matter. Most said no. The overtures only added to the friction within the firm.

“The work I do is high-stakes and challenging, requiring both toughness and precision,” Ms. Kaplan said in a statement to The Times. Because she has taken on “some of the world’s biggest bullies,” she added, “there are people who don’t like me, which comes with the territory, particularly when you are a woman. I am proud of my record as a lawyer, colleague and mentor.”