The top staff investigator on the House committee scrutinizing the Jan. 6 attack on the Capitol has been fired by the state’s new Republican attorney general from his position as the top lawyer for the University of Virginia, from which he was on leave while working on the congressional inquiry.

The office of the attorney general, Jason S. Miyares, said the firing of the investigator, Timothy J. Heaphy, was not related to the Jan. 6 investigation, but the move prompted an outcry from Democrats in the state, who accused him of taking the highly unusual action as a partisan move to further former President Donald J. Trump’s attempts to undermine the committee’s work.

“This is purely payback for Jan. 6 — there is no other reason that makes any sense,” said Scott Surovell, a top Democrat in the Virginia State Senate, who said that he knew of no other similar example in recent history where a new attorney general had immediately removed a school’s top lawyer. “In our state, we normally leave those decisions to the school’s board of visitors and president.”

Victoria LaCivita, a spokeswoman for Mr. Miyares, said: “The decision had nothing to do with the Jan. 6 committee or their investigations.”

In Virginia, the attorney general oversees a range of lawyers across the state, including the top lawyers at the colleges and universities that make up the vast public higher education system. The posts are typically held by career lawyers who are rarely replaced when new attorneys general take over.

In addition to dismissing Mr. Heaphy, Mr. Miyares also had the top lawyer at George Mason University removed.

Mr. Heaphy, a registered Democrat, had been the top lawyer at the University of Virginia since 2018. He served as a United States attorney in Virginia during the Obama administration and is married to the daughter of Eric K. Shinseki, the retired Army secretary who served as President Barack Obama’s secretary of veterans affairs. In 2017, on behalf of the City of Charlottesville, he completed a highly critical report of how the police handled the white nationalist rally that turned violent and led to the death of one woman and injured dozens.

In a written statement, the University of Virginia sidestepped the issue of whether his dismissal had been motivated by politics, but made clear that it had no role in it.

“University leaders are grateful to Tim for his outstanding service to our community and disappointed to see it come to an end,” said Brian Coy, a spokesman for the university. “If you have further questions about this matter, I would check with the attorney general’s office, as this was their decision to make.”

Mr. Heaphy — who attended undergraduate and law school at the University of Virginia, who has long lived in Charlottesville and whose son attends the school — declined to address why he was dismissed, saying that he was “disappointed” that his time at the university had come to an end and that he was confident that the school would continue “to thrive in the days to come.”

In two statements released on Sunday, the attorney general’s office said the firing was unrelated to the Jan. 6 inquiry. In the first, to The Associated Press, Ms. LaCivita said that Mr. Heaphy had been a “controversial” hire and that the “decision was made after reviewing the legal decisions made over the last couple of years.”

“The attorney general wants the university counsel to return to giving legal advice based on law, and not the philosophy of a university,” she added.

In a subsequent statement, Ms. LaCivita said: “It is common practice for an incoming administration to appoint new staff that share the philosophical and legal approach of the attorney general. Every counsel serves at the pleasure of the attorney general.”

One top Virginia Republican said that Mr. Heaphy had angered some Republicans in the state by acting too independently in his job at the university and for his role in the university’s decision in 2020 to allow a student to post a highly critical sign about the school on their door. Mr. Heaphy had privately made the case to the school’s president that while the profanity on the sign was offensive, removing it would have infringed upon the student’s First Amendment rights.

On the House committee, Mr. Heaphy has worked behind the scenes, overseeing a staff of dozens of investigators who are examining how Mr. Trump and his allies sought to overturn the election and the Jan. 6 attack on the Capitol.

Mr. Heaphy is close to the committee’s vice chairwoman, Representative Liz Cheney, Republican of Wyoming, who has taken a highly aggressive approach to the inquiry.