WASHINGTON — Jared Kushner, President Trump’s son-in-law and senior adviser, has been granted his permanent security clearance, a person briefed on the matter said on Wednesday, ending a period of uncertainty that had fueled questions about whether Mr. Kushner was in peril in the special counsel investigation.

Mr. Kushner is a senior presidential aide with a prominent role in Middle East diplomacy. But his F.B.I. background checks dragged on for a year and became one of many political distractions for the White House. Even some inside the administration suspected that Mr. Kushner’s delay reflected legal problems on the horizon.

The permanent clearances make Mr. Kushner, who is married to Mr. Trump’s daughter Ivanka Trump, eligible to view some of the United States’ most closely guarded secrets, including the daily intelligence briefing that Mr. Trump receives and the delicate intelligence on the Israelis and the Palestinians that former diplomats said can be valuable in negotiations. Top-secret clearances are typically required for people viewing foreign intelligence or sitting in on high-level White House meetings.

White House officials were adamant that the lengthy process was not unusual for a government official who has a complicated financial history and many foreign contacts. But with the special counsel investigating some of Mr. Kushner’s meetings with Russian officials, it left open the question of whether investigators had uncovered evidence that made him a security threat.