John R. Bolton, a former top adviser to President Trump who became one of his most outspoken critics, is expected to plead guilty Friday morning to mishandling classified information in a case that could send him to prison.

Mr. Bolton, is set to appear in Federal District Court in Greenbelt, Md., and admit to a single charge of illegal retention of classified information over notes he compiled for a book that excoriated Mr. Trump, according to people with knowledge of the terms of a plea deal with prosecutors.

Under the plea deal, which must still be approved by a judge, Mr. Bolton could be incarcerated for up to five years, according to the people with knowledge of it. The deal also includes a fine of more than $2 million, they said, describing settlement terms that have not yet been made public on the condition of anonymity. If Mr. Bolton had gone to trial and lost, he could have faced decades in prison.

When he was first indicted, Mr. Bolton sought to frame the case against him as part of a push by the president to misuse the Justice Department to punish his perceived political enemies. The case against Mr. Bolton, however, began in the first Trump administration and gained momentum during the Biden administration, as investigators gathered additional evidence.

The original 18-count indictment against Mr. Bolton accused him of using personal email and a messaging app to share more than 1,000 pages of notes, which included national defense information, with two family members who did not have security clearances.

The accusations against Mr. Bolton center on his notes for “The Room Where It Happened,” his 2020 memoir about his time as Mr. Trump’s national security adviser. Those relatives were Mr. Bolton’s wife and daughter, according to people with knowledge of the matter, who spoke on the condition of anonymity to describe details of the case that were not in court filings.

According to the indictment, Mr. Bolton’s notes revealed that he understood that he was documenting intelligence secrets. One entry began, “The intel briefer said,” while another read, “While in the Situation Room, I learned.”

The first Trump administration fought unsuccessfully to prevent the publication of Mr. Bolton’s book, but the criminal investigation ultimately focused not on what was in the published manuscript, but instead what Mr. Bolton wrote in private notes and correspondence.

Unlike some other investigations involving classified information, including charges filed in 2023 against Mr. Trump, Mr. Bolton was not accused of retaining the secret documents themselves, but rather of keeping diaries and sending emails that mentioned details of his daily work in national security.

Mr. Bolton’s emails, however, were later hacked by someone associated with the government of Iran, the indictment said.

“A representative for Bolton notified the U.S. government of the hack in or about July 2021,” according to the filing, “but did not tell the U.S. government that the account contained national defense information, including classified information, that Bolton had placed in the account from his time as national security adviser.”

One section of the indictment described Mr. Bolton apparently being taunted by his hacker. A message on July 25, 2021, warned, “I do not think you would be interested in the F.B.I. being aware of the leaked content of John’s email (some of which have been attached).”

The email went on to declare, “This could be the biggest scandal since Hillary’s emails were leaked, but this time on the G.O.P. side! Contact me before it’s too late.”

A representative for Mr. Bolton forwarded the email to the F.B.I.