President-elect Joe Biden has chosen California Attorney General Xavier Becerra (D) to lead the Department of Health and Human Services, a critical position in the coalescing administration for which fighting the coronavirus pandemic looms as the most urgent mission once Biden takes office next month.

In selecting Becerra, a 24-year member of Congress before taking the attorney general post, Biden picked someone with an unorthodox background for HHS secretary.

The job running the sprawling department often has gone to governors, and public health officials have been urging the Biden transition team to select someone with expertise in medicine, given that the raging pandemic will remain front and center for many months.

But Biden had also been under pressure to select more Latinos in his Cabinet. Becerra becomes the second designated nominee who is Latino, after Alejandro Mayorkas, Biden’s pick for homeland security secretary. The choice of Becerra, first reported by the New York Times, was confirmed Sunday night by three individuals familiar with the decision who spoke on the condition of anonymity to discuss the selection.

Also, three individuals with knowledge of Biden’s choice said he has picked Rochelle Walensky, an infectious-disease specialist at Massachusetts General Hospital, for the job of director of the Centers for Disease Control and Prevention. A professor of medicine at Harvard Medical School, she is well-respected for her work, including on the comparative effectiveness of treatment for HIV and AIDs.

A spokesman for the Biden transition declined to comment Sunday night.

The HHS position is the third role at the helm of the incoming administration’s pandemic response to be filled in the past few days, though none has been publicly announced by Biden. Last week, the president-elect offered an expanded version of the job of surgeon general to Vivek H. Murthy, a co-chair of the administration’s covid-19 advisory board, who would reprise a role he held during the Obama presidency and a few months into President Trump’s tenure. And Biden is looking to Jeff Zients, co-chair of the transition, as the White House’s coronavirus coordinator. Zients led the White House’s National Economic Council under President Barack Obama.

Becerra’s selection is a break from a pattern in which the president-elect is selecting people as his right-hand advisers who have lengthy working relationships with him from earlier in his career, including his eight years as Obama’s vice president. But Becerra, 62, has been under consideration for three possible positions in the Biden Cabinet, including attorney general, according to one individual familiar with the selection process. He also was a potential successor to Vice President-elect Kamala D. Harris when she leaves her spot in the Senate.

The idea of Becerra as HHS secretary “all picked up late in the week. It started to snowball,” according to the individual, who spoke on the condition of anonymity because they lacked authorization to discuss the transition’s personnel goings-on.

Another person familiar with the selection, also speaking on the condition of anonymity about matters that are not public, said that Biden offered Becerra the HHS secretary’s job Friday.

According to this person, the president-elect chose him because he regarded the attorney general of the country’s most populous state as someone who has used that platform and earlier roles to expand access to health care.

HHS is one of the government’s largest departments, with several agencies within it that are crucial to the federal response to the pandemic, which has sickened nearly 15 million people in the United States and killed 281,000. In addition to the CDC, they include the Food and Drug Administration, the National Institutes of Health and the Centers for Medicare and Medicaid Services. The department contains many other units, such as the agency that oversees welfare, that are less central to the pandemic response.

In a transition that has had orderly rollouts in the past two weeks of Biden’s senior national security team and then his economic team, the question of who would become HHS secretary has appeared more complex. A few people who initially were widely regarded as contenders ended up not being among the finalists. One of them was New Mexico Gov. Michelle Lujan Grisham (D). The person familiar with the selection said she was considered for several Cabinet roles but ultimately chose not to join the incoming administration because of the severity of the coronavirus outbreak in her state.

During the Trump era, Becerra has been among the most outspoken state attorneys general, leading coalitions of Democratic colleagues in challenges to the current administration’s policies on immigration, the environment and health care, suing the federal government more than 100 times since taking office.

Others whose name rose and fell in the HHS secretary rumor mill included Murthy, who wanted the job, and Rhode Island Gov. Gina Raimondo (D). Several new names, including Becerra’s, began to surface in the latter part of last week.

Notably, he has been the lead attorney general in a multistate fight to preserve the Affordable Care Act in a case that is now before the Supreme Court.

He is the son of Mexican immigrants and the first in his family to graduate from college. Becerra left the House, where he had represented Los Angeles since 1993, when he was appointed in 2017 to fill what had been Harris’s job before she won a Senate seat. He won election to the post the following year.

The person familiar with the selection said that Biden likes the fact that, like himself, Becerra has working-class roots and educational attainments beyond those of his parents.

As a member of the House, Becerra was a member of the Ways and Means Committee, a panel with jurisdiction over large federal health-care programs. Beyond championing the preservation of the ACA with fellow Democrats, the person said, Becerra has worked with Republican state attorneys generals on other significant issues. They include widening access to remdesivir and other therapies for covid-19, the illness caused by the coronavirus.

The person noted that, during the campaign, Becerra supported the idea of changing to a single-payer health care system, colloquially known as Medicare-for-all, which Biden does not favor. But Becerra is now prepared to support the president-elect’s preferred path for expanding health coverage by expanding the ACA.

His selection drew swift praise from leading Latino voices.

“Xavier Becerra is a dedicated, hard-working public servant who has led the fight against the Trump administration’s attacks on the Affordable Care Act,” said Rep. Joaquin Castro (D-Tex.), chairman of the Congressional Hispanic Caucus, which has lobbied Biden to pick Latinos for his Cabinet. “As the Latino community has been devastated by covid-19, Attorney General Becerra has worked to make sure all Americans get the health-care coverage they deserve. The Congressional Hispanic Caucus congratulates Xavier and his family on this historic nomination.”

Janet Murguia, president of UnidosUS, a leading Latino advocacy organization, said: “Xavier Becerra has excelled as a member of the U.S. Congress, as California attorney general, and he will bring the same level of knowledge, talent, energy, commitment and compassion to his new role as HHS secretary during the greatest public health crisis in our time. . . . While it is not exactly where we thought they would use his excellent skills and track record, it is another historic and stellar choice by President-elect Joe Biden.”

However, a senior Republican aide on Capitol Hill said Sunday night that the GOP plans to focus on Becerra’s support for Medicare-for-all and whether he truly has expertise in health-care policy.

In being chosen to lead the CDC, Walensky will take over an agency within HHS that was once the world’s most admired public health agency but has suffered a loss of credibility under the Trump administration, which has sidelined it during the pandemic.

Some senior leaders at the CDC were surprised the choice was not someone with more ground-level public health experience, according to an individual familiar with the decision. However, according an individual close to the transition who spoke on the condition of anonymity to discuss the pick, Walensky has “unparalleled credibility on infectious diseases and brings fresh leadership. . . . There are plenty of experienced managers at CDC she can rely on.”

Matt Viser, Lena H. Sun and Annie Linskey contributed to this report.