President-elect Donald J. Trump on Saturday chose Chad Chronister, a veteran Florida sheriff, to be his administration’s top drug enforcement official, tasking him with delivering on campaign promises to curb the flow of fentanyl and other illegal drugs into the country.

Appointed sheriff of Hillsborough County in 2017 by Gov. Rick Scott, the Republican who is now a senator, and re-elected twice, Sheriff Chronister has served on state and regional law enforcement boards, including the Florida Statewide Drug Policy Advisory Council.

“For over 32 years, Sheriff Chad Chronister has served the Hillsborough County Sheriff’s Office and received countless awards for keeping his community SAFE,” Mr. Trump wrote in a social media post announcing his choice.

Mr. Trump repeatedly highlighted the opioid crisis during his campaign, framing it as a major national security threat. The president-elect has threatened to impose damaging tariffs on China, Mexico and Canada in an effort to curb migration and the trafficking of drugs, particularly fentanyl, across U.S. borders.

As head of the Drug Enforcement Administration, Sheriff Chronister will play a central role in addressing the escalating tensions surrounding fentanyl being brought into the United States.

In response to the announcement, Sheriff Chronister posted on social media, “It is the honor of a lifetime to be nominated” for the position by Mr. Trump. He added, “I am deeply humbled by this opportunity to serve our nation.”

The D.E.A., an arm of the Justice Department, said in its fiscal year 2025 budget request that 2023 was the highest year for fentanyl seizures since the agency’s inception more than half a century ago. In addition, the agency confiscated more than 77 million fentanyl pills and nearly 12,000 pounds of fentanyl powder. The agency has more than 10,000 employees, with offices in the U.S. and in more than 60 different countries. It has a budget of more than $3 billion.

For comparison, Sheriff Chronister’s department in Florida, one of the largest sheriff’s offices in the state, has a 2024 budget of about $600 million and oversees more than 3,500 employees.

Sheriff Chronister’s father-in-law, Edward J. DeBartolo Jr., received a pardon from Mr. Trump in 2021. Mr. DeBartolo, a former owner of the N.F.L.’s San Francisco 49ers, pleaded guilty in 1998 to concealing an extortion plot. Though he avoided prison, he was fined $1 million and was suspended for a year by the N.F.L.