Prolific stock trades by David Perdue involved companies within his committees’ oversight.

Senator David Perdue, the Georgia Republican facing a runoff election that could determine the control of the Senate, made 2,596 stock trades in one term in office, including, at times, 20 or more transactions in a single day.

The number of trades far outpaced those made by his Senate colleagues, a Times analysis found. And the timing of some of them have raised questions about conflicts of interest, drawing attention to the senator’s investment portfolio just a few weeks before a highly consequential runoff election.

The Justice Department had investigated the senator for possible insider trading in his sale of more than $1 million worth of stock in a financial-analysis firm, Cardlytics. Ultimately, prosecutors declined to bring charges.

The Times analyzed data compiled by Senate Stock Watcher, a nonpartisan website that aggregates publicly available information on lawmakers’ trading. Mr. Perdue’s transactions -mostly in stocks but also in bonds and funds — accounted for nearly a third of all senators’ trades reported in the past six years.

The data also shows the breadth of trades Mr. Perdue made in companies that stood to benefit from policy and spending matters that came not just before the Senate as a whole, but before the committees and subcommittees on which he served.

As a member of the Senate’s cybersecurity subcommittee, Mr. Perdue cited a frightening report about hackers overseas that pose a threat to U.S. computer networks. The report was done by a California-based company called FireEye, a federal contractor with stock Mr. Perdue bought and sold 61 times since 2016. At one point he owned as much as $250,000 worth of shares in the company.