The Senate on Thursday confirmed Dr. Mehmet Oz, the celebrity TV doctor, 53-45 and along party lines to lead Medicare and Medicaid, which insure nearly half of all Americans.

The future of both programs is the subject of fierce debate: Republicans are contemplating significant cuts to Medicaid, which provides health care to low-income Americans. The Trump administration and G.O.P. lawmakers have proposed sizable reductions in Medicaid spending in part to find savings to pay for President Trump’s tax-cut package.

Dr. Oz, 64, has for years been a vocal proponent of Medicare Advantage, the private insurance plans for older Americans, despite federal inquiries and lawmakers’ concerns that insurers have overbilled the government by tens of billions of dollars a year. He promoted it on his TV show and acted as a broker for one company that sells the plan.

At his confirmation hearing before the Senate Finance Committee last month, he seemed to acknowledge problems with Medicare Advantage, and tried to reassure senators that there was a “new sheriff in town.”

Democrats on the committee grilled him at length about the potential steep cuts to Medicaid, which could result in a substantial number of people becoming ineligible for health coverage.

In recent days, Health Secretary Robert F. Kennedy Jr. has overseen deep cuts to the Health and Human Services Department, including laying off roughly 10,000 employees on top of another 10,000 buyouts, retirements and departures early on in the new Trump administration.

The cutbacks also affect Dr. Oz’s agency, the Centers for Medicare and Medicaid Services, which has a budget of about $1.5 trillion in annual spending. Still, Dr. Oz has given few clues as to what if any changes he has planned.

Dr. Oz’s ability to secure enough votes for confirmation was up in the air until recently. Then, earlier this week Senator Josh Hawley, the Missouri Republican, said he had decided to support his nomination because Dr. Oz told him that he would no longer support transgender care for minors and was “unequivocally pro-life.” Mr. Hawley had publicly said he was withholding his support over Dr. Oz’s previous positions on these issues.

Senators largely sidestepped criticism of Dr. Oz’s extensive and often murky financial ties to companies he will oversee in his new position.

He and his wife are wealthy. All told, his business and family ventures are valued in the neighborhood of roughly $90 million to $335 million.

In an attempt to avoid conflicts, he announced in February he would sell his interest in more than 70 companies and investment funds.

He has made tens of millions of dollars over the years pitching dietary supplements and promoting health-related companies on his television show.

The investments he said he planned to sell included stakes in UnitedHealth Group, the giant conglomerate that is the nation’s largest provider of private Medicare plans; Inception Fertility Holdings, a privately held company that operates a chain of clinics; and Amazon, which has a vast reach that now includes an online pharmacy and sells myriad medical devices and equipment.

In addition, he pledged to resign from various paid advisory jobs.

Still, the breadth of his financial ties to countless health-related companies has prompted lawmakers and ethics experts to express doubts about his ability to be independent.