Robert F. Kennedy Jr. was sworn in as health and human services secretary after his confirmation Thursday, giving him license to “go wild” on health and putting the last of President Trump’s contentious nominees into place so his Cabinet can reset the federal government.

The Senate’s 52-48 vote capped an unlikely rise for Mr. Kennedy, a vaccine skeptic who assembled a robust following and worked overtime to assure senators he would not discredit proven cures or settled science.

Mr. Trump wasted no time in putting Mr. Kennedy to work. He said the secretary will lead the Presidential Commission to Make America Healthy Again.

“Bobby is going to lead a great national mission to make America healthy again,” Mr. Trump said after Supreme Court Justice Neil M. Gorsuch delivered the oath of office to Mr. Kennedy. “I think he’s going to do things that really make us very proud of this day.”

Mr. Kennedy thanked the president for having confidence in him and a deep concern for Americans’ health.

“I have prayed each morning for the past two decades for God to put me in a position to solve the childhood chronic disease epidemic, and now, thanks to you, Mr. President, we will make this promise a reality​,” he said.

Mr. Kennedy was the last of Mr. Trump’s most hotly contested nominees to win Senate confirmation.

Former Rep. Tulsi Gabbard was confirmed as director of national intelligence on Wednesday, and Pete Hegseth was confirmed weeks ago as defense secretary with a tiebreaking vote from Vice President J.D. Vance.

Mr. Kennedy, Ms. Gabbard and Mr. Hegseth plan aggressive overhauls of their respective departments or offices, which they say have drifted ​off track.

At the White House, Mr. Kennedy vowed to end the cozy relationship between drug companies and U.S. officials who regulate them.

He promised to focus on “ending the corporate capture at those agencies, getting rid of the people on those panels with conflicts of interest.”

He has proposed shifting resources away from fighting infectious diseases and toward research that promotes general health.

Republican senators found that platform, combined with Mr. Trump’s clout, hard to ignore, especially as audience members loudly applauded him in hearing rooms on Capitol Hill.

Republican senators rallied around Mr. Kennedy on Thursday. The exception was Sen. Mitch McConnell of Kentucky, who battled polio as a child and said he would “not condone the relitigation of proven cures.”

Senate Democrats, many of whom admired Mr. Kennedy’s famous political family, also voted against his nomination. They dubbed him a danger to American health who would invite the return of measles and other vaccine-preventable diseases.

The sprawling Department of Health and Human Services, with a $1.7 trillion budget, oversees food and drugs, disease-fighting efforts and major insurance programs such as Medicare and Medicaid.

Mr. Kennedy built his career as an environmental lawyer, activist and anti-vaccine Children’s Health Defense chairman. His predecessors include former members of Congress and a pharmaceutical executive.

Mr. Kennedy built a diverse coalition of support during his confirmation battle, including liberal “crunchy granola moms” who sought natural alternatives to some drugs or consumer products and conservatives skeptical of the government’s narrative during the COVID-19 crisis.

“Bobby created a nationwide movement made up of millions and millions of mothers and fathers and young people and concerned citizens of every background who want to end this horrible chronic disease crisis that exists in America,” Mr. Trump said.

Still, Mr. Kennedy’s past comments on vaccines, particularly an unproven link to autism, sparked alarm.

The nominee said he wanted to ensure reasonable vaccine safety data, although some senators felt he was churning out settled science.

He also raised eyebrows by suggesting that municipalities stop adding fluoride to drinking water. Dentists say fluoride is essential for preventing cavities in children, but critics of added fluoride say the mineral is available elsewhere and high levels have been linked to lower IQ.

Democrats said Mr. Kennedy can’t be trusted.

“It’s almost as if Mr. Kennedy’s beliefs, history and background were tailor-made to be the exact opposite of what the job demands,” said Senate Minority Leader Charles E. Schumer, New York Democrat.

Mr. Kennedy’s nomination seemed tenuous at best weeks ago. Conservatives such as former Vice President Mike Pence said Mr. Kennedy could not be trusted to promote pro-life policies. Pharmaceutical stocks dropped because of Mr. Kennedy’s past comments on vaccines and focus on healthy lifestyles instead of miracle drugs.

Yet, like other Trump nominees, Mr. Kennedy muscled through his confirmation battle.

Mr. McConnell has been a notable voice of dissent. He also voted against Mr. Hegseth and Ms. Gabbard, drawing a rebuke from the White House.

“He’s not equipped mentally,” Mr. Trump said of Mr. McConnell. “I was the one that got him to drop out of the leadership position.”

Mr. McConnell, explaining his vote against Mr. Kennedy, said his experiences as a child with polio underscored the importance of vaccines.

“I will not condone the relitigation of proven cures, and neither will millions of Americans who credit their survival and quality of life to scientific miracles,” he said. “Individuals, parents and families have a right to push for a healthier nation and demand the best possible scientific guidance on preventing and treating illness. But a record of trafficking in dangerous conspiracy theories and eroding trust in public health institutions does not entitle Mr. Kennedy to lead these important efforts.”

Mr. Kennedy, a son of the late Attorney General Robert F. Kennedy, ran for president as a Democrat and then switched to an independent in the 2024 race. He dropped out and supported Mr. Trump.

The president repaid that support by nominating Mr. Kennedy to HHS and encouraging senators to fall in line.

Sen. Bill Cassidy, Louisiana Republican, said he received an unusual commitment from Mr. Kennedy to coordinate health messaging and avoid actions that would cast doubt on common vaccines.

Another potential Republican holdout, Sen. Susan M. Collins of Maine, said she persuaded Mr. Kennedy to take a closer look at Trump-led efforts to cap “indirect costs” linked to National Institutes of Health grants. She said the cap was arbitrary and would lead to job losses.

Mr. Kennedy “has promised that as soon as he is confirmed, he will reexamine this initiative that was implemented prior to his confirmation,” Ms. Collins said.

Lobbyists for major industries facing scrutiny from Mr. Kennedy struck a collaborative tone.

“Keeping consumers and their families safe is our No. 1 priority,” said Sarah Gallo, a senior vice president for federal affairs at the Consumer Brands Association, whose members include food and beverage companies. “As the largest domestic manufacturing employer, supporting more than 22 million American jobs, we stand ready to work with Secretary Kennedy and qualified experts within HHS to support public health, build consumer trust and promote consumer choice.”

The Pharmaceutical Research and Manufacturers of America, a key drug company lobby, urged Mr. Kennedy to reduce “the burden of chronic disease” and scrutinize middlemen, or pharmacy benefit managers, who are sometimes blamed for high drug costs.

In turn, the pharmacy benefit managers lobby, the Pharmaceutical Care Management Association, urged Mr. Kennedy to address high drug company prices and patent system abuses that block cheaper alternatives to brand-name drugs.

• Tom Howell Jr. can be reached at thowell@washingtontimes.com.