A top political adviser to Gov. Kathy Hochul of New York abruptly informed colleagues that he would resign on Sunday, citing a New York Times report that called into question his political counsel and described a toxic work environment under him.

The adviser, Adam C. Sullivan, was not a state government employee but had been the de facto head of Ms. Hochul’s political operation, as well as a trusted and well-compensated confidant for more than a decade. He oversaw her 2022 campaign from his home in Colorado, and she had deputized him to help steer the beleaguered state Democratic Party.

In an email Sunday to colleagues, including the state party chairman, Mr. Sullivan apologized for behavior that included belittling and marginalizing his subordinates and said he and the governor agreed he should relinquish his responsibilities “for the foreseeable future.”

“In retrospect, I can see the toll that the campaign took on me,” he wrote in the email, sent just after 5 p.m. “And after some serious thinking, I think it best if I take some time away from politics and the campaign environment and get healthy.”

Ms. Hochul, a Democrat who had praised Mr. Sullivan just last week, confirmed his resignation in a separate brief statement. She did not elaborate on who might fill his place, and Mr. Sullivan did not immediately respond to requests for additional comment.

“I was disappointed by what was described in The New York Times story about Adam, and he and I agreed that he should step back,” Ms. Hochul said.

The departure comes at a politically fraught time for the governor, as she is putting the final touches on a $229 billion state budget that is a month overdue. Questions about Mr. Sullivan’s political acumen and treatment of other Hochul aides had become a distraction in Albany in recent days, with labor leaders, lawmakers and lobbyists questioning how Ms. Hochul could continue relying on him.

Some fellow Democrats said on Sunday said that Ms. Hochul had made the right decision.

“Given that nobody knew what Mr. Sullivan was responsible for, perhaps his departure will add clarity to her organizational chart,” said Brad Hoylman-Sigal, a Democratic state senator from Manhattan. “Governor Hochul has a strong team on the second floor. This will improve the lines of communication between the governor and the Legislature.”

A friend and adviser to Ms. Hochul since her 2011 special election to Congress, Mr. Sullivan, 42, amassed considerable influence after she unexpectedly became governor in August 2021. He helped build her administration, oversaw her widely criticized campaign for a full term and recently took a more active role with the state party.

During the campaign, he pushed back against other advisers who wanted to see Ms. Hochul more actively address fears about crime — a potent line of attack used by Republicans.

Mr. Sullivan argued that crime was a losing issue for a Democratic governor, and advised Ms. Hochul to stay focused on abortion rights, an issue he believed would motivate voters. Ms. Hochul narrowly won, but national Democrats have blamed her approach for costing House seats in New York.

Ms. Hochul does have other important advisers who have played a role in building her political team, including Karen Persichilli Keogh, her top government aide, and Jefrey Pollock, her longtime pollster. But none played quite the role Mr. Sullivan did.

Without a defined job title and no social media profile, Mr. Sullivan operated largely out of public view from his home 1,700 miles away in Leadville, Colo. He had few relationships with important political actors in the state and even his generous compensation was murky.

Ms. Hochul’s campaign reported paying $50,000 since 2021 to a limited liability company that Mr. Sullivan controls, “ACS Campaign Consulting.” But The Times found that he had earned $500,000 or more in a secretive arrangement where he received a portion of what the campaign spent on TV ads.

Mr. Sullivan also faced dissent from within Ms. Hochul’s campaign team and the executive chamber. The Times’s report cited more than 15 colleagues who said that Mr. Sullivan had disparaged subordinates, especially young women, froze out aides who disagreed with him and often shifted blame to others when the campaign faltered.

The aides and advisers who spoke to The Times all requested anonymity for fear of retribution, but said they believed Mr. Sullivan was pulling down Ms. Hochul’s political standing.

In his email on Sunday, Mr. Sullivan apologized “to anyone who felt harmed in any way by my behavior.”

He also suggested the break would be permanent.

Ms. Hochul would govern “without me interfering in any way,” he said. “I look forward to watching her success from afar.”