WASHINGTON—A top FBI official who helped oversee two politically sensitive investigations related to the 2016 presidential campaign is retiring from government service.

Bill Priestap, who currently serves as assistant director of the Federal Bureau of Investigation’s counterintelligence division, will leave his post by the end of the year. Mr. Priestap, a 20-year veteran of the bureau, worked on organized crime and drug cases in Chicago before rising through the national security ranks of the agency after the terrorist attacks of Sept. 11, 2001.

Mr. Priestap’s retirement is unrelated to the controversies over the handling of the 2016 investigations, according to a person familiar with the matter. He “became eligible to retire and has chosen to do so after 20 years of service,” the FBI said in a statement.

The federal government allows some employees, including FBI agents, to retire with full benefits if they are 50 or older and have at least two decades of service.

During the 2016 campaign, Mr. Priestap was one of several officials at the center of two politically volatile probes: the investigation into Hillary Clinton’s handling of classified information, and a counterintelligence inquiry into whether associates of then-candidate Donald Trump colluded with the Russian government.


After Mr. Priestap’s departure, none of the high-ranking bureau officials involved in the two investigations will remain with the bureau. FBI director James Comeywas fired by President Trump last year, and Deputy Director Andrew McCabewas later dismissed by then-Attorney General Jeff Sessions over his contacts with the media, days before he was eligible to retire with benefits.

Peter Strzok, the chief of the counterespionage section, left the FBI this year after it emerged that he had sent disparaging text messages about Mr. Trump.

Top bureau officials, especially those with national security experience, are in high demand in private-sector fields like cybersecurity, defense contracting and private intelligence. Mr. Priestap’s future plans aren’t known.

Documents and congressional testimony show that Mr. Priestap was in the inner circle of FBI decision makers for both investigations. According to emails released by Congress, Mr. Priestap helped Mr. Comey edit a 2016 public statement on the investigation into Mrs. Clinton, who didn’t face charges, though Mr. Comey said she had been careless with classified material.


Mr. Priestap also supervised Mr. Strzok, and a June watchdog report said the Russia investigation was under Mr. Priestap’s supervision. Special Counsel Robert Mueller took over handling the probe last year.

A memo prepared by House Republicans, which criticized FBI decisions during the 2016 election, indicated that Mr. Priestap was involved in efforts to verify a dossier of salacious, unconfirmed information concerning Mr. Trump’s ties to Russia. The dossier was used, in part, to obtain a secret surveillance warrant against a one-time Trump campaign adviser, according to the memo.

The Clinton and Trump investigations have come under enormous political scrutiny, with partisans on each side saying the bureau mishandled the inquiries.

Many Republicans, including Mr. Trump, have said that the FBI should have charged Mrs. Clinton with a crime. They have further accused the bureau of conducting illegal surveillance on Trump advisers.


The FBI counterintelligence investigation into Russian activity was absorbed into the Mueller probe in 2017—an investigation that Mr. Trump repeatedly called a partisan witch hunt.

Democrats have expressed frustration that the FBI criticized Mrs. Clinton in announcing its decision not to prosecute her, a departure from normal practice. They have also criticized Mr. Comey for reopening the Clinton investigation shortly before Election Day after obtaining new evidence, with some saying that it cost Mrs. Clinton the election.

Democrats have also complained that the FBI revealed that Mrs. Clinton was under investigation but didn’t disclose that an investigation was under way regarding Mr. Trump’s associates until after Election Day.

Write to Byron Tau at byron.tau@wsj.com