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 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.”