A veteran administrator will succeed Alberto Carvalho as the head of the Los Angeles Unified School District, trustees announced on Wednesday, moving to restore stability after the embattled superintendent’s resignation.

The administrator, Andres Chait, 51, began his career as an elementary teacher and worked his way to the top ranks of the nation’s second-largest school system over nearly three decades. He had held the superintendent role on an acting basis since late February, when Mr. Carvalho was placed on paid leave.

“Over the past few years, but particularly in these last four months, I have seen firsthand the student-centered focus that guides our actions,” Mr. Chait said at a meeting of the school board. “As we face a number of challenges, I could genuinely feel that folks were rooting for our shared success.”

The trustees regarded Mr. Chait, a self-described “proverbial lifer with L.A.U.S.D.,” as a steady and capable hand at an uncertain fiscal and political moment. They voted unanimously Wednesday to make his permanent appointment effective immediately.

“The board’s decision reflects the confidence in Mr. Chait’s leadership, his decades of service to Los Angeles Unified and his demonstrated ability to guide the district during this period of transition,” the board president, Scott Schmerelson, said as supporters in the audience applauded.

Mr. Carvalho was named to the post after a monthslong national search and had just renewed his four-year contract. Mr. Chait’s contract will not be made public until August. His salary as acting superintendent was about $396,000. Mr. Carvalho was paid $440,000 a year.

Mr. Carvalho was hired in 2021 as the district emerged from the pandemic, coming from Miami as a national leader in public education. He was effectively sidelined, however, after the F.B.I. raided his Los Angeles home and his office in February amid an investigation into the district’s dealings with an A.I. start-up.

Federal authorities have not charged Mr. Carvalho, nor said exactly who or what is under investigation. Mr. Carvalho, through his lawyers, has denied wrongdoing. As speculation mounted that Mr. Carvalho might not return from leave, at least four members of his upper management team, including at least two who followed him to Los Angeles from Miami, retired or resigned.

Terms of his potential departure have been under negotiation for months. In a letter sent Sunday to the district and members of the school board, Mr. Carvalho said he was resigning now, because “our schools must remain focused on students and learning without distraction.”

“Over the past four years, together, we have made historic progress — gains that belong to our students, our educators, staff and our communities,” Mr. Carvalho said. “Placing students first has always guided my work.”

The uproar has nonetheless created months of uncertainty and turmoil in the sprawling district, which employs more than 83,000 people and serves about 400,000 students, most of them from working-class Latino and immigrant families.

Immigration raids have increased absenteeism and stirred fears for student safety. Federal budget cuts and declining enrollment have posed an ongoing fiscal challenge. So has organized labor, a powerful political force in California.

In April, two months after Mr. Chait became the acting superintendent, the district narrowly averted a multiple-union strike that had been partly set in motion by a statewide labor action led by the California Teachers Association.

Mr. Carvalho was often regarded as an outsider in the Los Angeles bureaucracy and had a tense relationship with labor leaders, but Mr. Chait, with an undergraduate degree in sociology from the University of California, Berkeley, and a master’s in education administration from California State University, Los Angeles, has spent his career in the system.

His most recent job had been chief of school operations, overseeing emergency management, school safety, athletics and other nonclassroom functions.

Mr. Chait vowed in his first public address “to ensure stability, continuity and strong leadership for our students, families and employees.”

Critics since then have questioned whether Mr. Chait had driven a hard enough bargain with the unions and whether the raises and health and pension benefits that he helped broker will force the district to resort to layoffs.

On Wednesday, Mr. Chait said that he was proud to have stewardship of an institution crucial to hundreds of thousands of young lives.

“Almost 30 years ago, I stepped into a kindergarten classroom at Queen Anne Elementary for the first time,” Mr. Chait said. “I was probably more nervous than the kids were, but I knew then that this was a place where I could make a positive difference in the lives of students and families. I have always known that there was no greater accelerator of change and opportunity than the schoolhouse and that is still true today.”