A handful of other senators drew similar scrutiny for their trades over the same period and were cleared in the spring and summer. Mr. Burr’s case proved far more complicated and included grand jury subpoenas and a search of his electronic storage accounts. At one point, the F.B.I. seized his cellphone — a highly invasive tactic for a sitting member of Congress that required signoff by Attorney General William P. Barr.

Mr. Burr, 65, insisted throughout that he had acted within the law, but preemptively stepped down from his Intelligence Committee post to avoid distractions and adopted a low profile in the Senate. He had already planned to retire when his term ends in 2022.

“Tonight, the Department of Justice informed me that it has concluded its review of my personal financial transactions conducted early last year,” Mr. Burr said in a statement. “The case is now closed. I’m glad to hear it. My focus has been and will continue to be working for the people of North Carolina during this difficult time for our nation.”