Jack Smith, the special counsel who brought two failed federal prosecutions against President-elect Donald J. Trump, resigned this week, according to a footnote buried in court papers — a remarkably muted conclusion to a fight that reshaped the nation’s legal and political landscape.

Mr. Smith, a former war crimes prosecutor who fought a bitter and protracted battle on two fronts with the Trump legal team but lost in both a district court and in the Supreme Court shaped by Mr. Trump, left his offices in Washington on Friday, according to a senior law enforcement official.

His departure was expected. Mr. Smith had signaled his intention to leave before Mr. Trump, who had threatened to fire and punish him, took office on Jan. 20.

In the end, Mr. Smith made no formal announcement. His spokesman had no comment.

The special counsel departed after his efforts in the courtroom were essentially rendered moot by Mr. Trump’s political victory in November. Under a Justice Department policy prohibiting the pursuit of prosecutions against a sitting president, Mr. Smith was compelled to drop both of the cases he had filed against Mr. Trump in 2023 — one in Florida, accusing him of mishandling a trove of classified documents, and the other in Washington, on charges of plotting to overturn the 2020 election.

Mr. Smith’s final week was marked by one more legal setback at the hands of Judge Aileen M. Cannon, the Trump-appointed jurist presiding over the Florida documents case: She temporarily blocked public release of his final report until at least Monday.

The monumental legal saga, which embittered Mr. Trump and steeled him for his remarkable return to power, ended with a single line at the bottom of the last page of a brief sent to Judge Cannon on Saturday: “The special counsel completed his work and submitted his final confidential report on Jan. 7, 2025, and separated from the department on Jan. 10.”

Mr. Smith’s resignation left unfinished one last step in the more than two-year odyssey he undertook by investigating and ultimately bringing charges against Mr. Trump: the release of a two-volume report detailing his decision-making in both criminal cases.

Mr. Trump’s lawyers and lawyers for his two co-defendants in the documents case have been fighting fiercely for the past week to stop the release of both volumes. In court papers, they have assailed the report as a “one-sided” and “unlawful” political attack against the president-elect and complained it unfairly implicates some unnamed “anticipated” members of his incoming administration.

The report amounts to Mr. Smith’s valedictory word on the work he started when he was first appointed in November 2022, shortly after Mr. Trump announced he was running again for president. It contains his explanations of why he brought the charges he did in the two cases as well as his legal reasoning for not bringing other charges.

Each of the cases died in different ways.

The classified documents case was dismissed outright by Judge Cannon in a July ruling that found — against decades of precedent — that Mr. Smith had been unlawfully appointed to his job as special counsel. While Mr. Smith’s deputies appealed that ruling, they dropped the challenge where Mr. Trump was concerned after he was re-elected, but not against his two co-defendants.

Around the same time, the Supreme Court hobbled the election interference case in a landmark ruling that granted Mr. Trump a broad form of immunity for official acts he took as president. The ruling not only called into question many of the allegations in Mr. Smith’s indictment, but more important, made it impossible to hold a trial on the charges before the election.

Earlier this week, the Justice Department said it did not intend to immediately release the volume of Mr. Smith’s report concerning the classified documents case because the prosecution of Mr. Trump’s former co-defendants, Walt Nauta and Carlos De Oliveira, continued. The department said it planned to show that part of the report in private to members of Congress and make it public only once all of the proceedings against the two men had been completed.

The Justice Department does, however, plan to release the volume concerning the election interference case as soon as possible. But lawyers for Mr. Nauta and Mr. De Oliveira have asked Judge Cannon to extend her order blocking the report.

The two investigations of Mr. Trump were initially conducted by regular federal prosecutors. Attorney General Merrick B. Garland placed Mr. Smith in charge of the cases after Mr. Trump announced his plans to run for president in order to put some distance between the inquiries and the Justice Department.

Mr. Smith was “the right choice to complete these matters in an evenhanded and urgent manner,” Mr. Garland said in announcing the appointment of the upstate New York native, who had been serving as the top prosecutor at The Hague investigating war crimes in Kosovo.

Mr. Smith, 55, cut an elusive figure. He granted no interviews and kept a low profile — appearing before reporters only briefly to read short statements affirming his intention to investigate Mr. Trump fairly and quickly.

“Adherence to the rule of law is a bedrock principle of the Department of Justice,” said Mr. Smith, in announcing the Florida indictments in August 2023. “And our nation’s commitment to the rule of law sets an example for the world. We have one set of laws in this country, and they apply to everyone.”

Now, Mr. Smith and the small team of veteran prosecutors who worked on the Trump cases may end up in the cross hairs of Republicans. Three of the Trump team lawyers he opposed have been given top positions in the Justice Department and the White House by Mr. Trump, who has repeatedly suggested that those who put him in the criminal dock should face consequences.

“I defeated deranged Jack Smith, he’s a deranged individual,” Mr. Trump told reporters in Florida this week. “We did nothing wrong. We did nothing wrong on anything.”

Some Democrats, including Representative Gerald E. Connolly of Virginia, the senior Democrat on the House Oversight Committee, have called on President Biden to issue a pre-emptive pardon of Mr. Smith and his team.