“I’m really looking forward to having more time to spend with my family, especially chasing around my toddler grandchild,” she wrote.

Multiple sources told the Globe that Walsh had not planned to stay in the role for more than two years. She will continue working as an adviser for the governor, though a state spokesperson did not respond when asked how long she would stay or if the position would be paid.

HHS’s $32 billion budget accounts for more than half of the state’s total expenditures. With more than 23,000 workers across 11 departments and MassHealth, HHS is responsible for programs including elder services, assistance for low-income families, state psychiatric hospitals, and support for the blind and deaf. Nearly one in three state residents receive services or support from at least one HHS department.

Mahaniah steps into an office attempting to maintain Massachusetts’ expansive social services programs despite existential threats from the Trump administration.

This week, MassHealth said 300,000 people are at risk of losing their insurance coverage over the next decade amid a $1 trillion cut to federal Medicaid spending. It is virtually guaranteed Mahaniah will be in the unenviable position of helping to decide which services to preserve, and which to curtail. There are guiding principles he will turn to, Mahaniah said in one of his first interviews since the state announced his appointment.

“Can we focus on the most vulnerable in our society, and can we assure that those most vulnerable have access to services?” he said.

Health care providers and experts described Mahaniah as a compassionate, knowledgeable veteran of the state’s health care system willing to tackle hard problems.

“He demonstrates a unique calm and certainty even in the most trying of times,” said Kaitlyn Kenney Walsh, vice president of policy and research at the Blue Cross Blue Shield of Massachusetts Foundation, an independent policy analysis organization.

The same federal legislation that contracted Medicaid access also put new restrictions on the HHS-managed Supplemental Nutrition Assistance Program, a food program for low-income families, putting 175,000 people at risk of losing some or all of their SNAP benefit, the Massachusetts Law Reform Institute estimated. The Department of Public Health, also overseen by HHS, is attempting to maintain Massachusetts’ high child vaccination rates despite federal funding cuts and is increasingly isolated as the Trump administration shrinks federal services that helped state experts track and contain emerging diseases.

The Healey administration reported HHS services have lost $118 million in federal funding so far this year.

“The health care and social services policy changes and funding cuts from the federal government are going to be devastating for Massachusetts,” Kenney Walsh said.

Meanwhile, HHS faces challenges from surging health care costs, an overburdened mental health system, and a child welfare system among the most stressed in the country.

Mahaniah described himself as just one of the decision makers who will determine Massachusetts’ path, “one musician in the orchestra,” he said.

His priorities include making Massachusetts’ health and social service programs less siloed.

“People that use our programs, most of them don’t just use one program,” he said. “I’m very interested in figuring out how to have the system be a little bit more customer-centric.”

Mahaniah has a background as a practicing physician in addiction and primary care, and before joining HHS he worked as chief executive of Lynn Community Health Center.

In a statement issued Friday, the Lynn center said Mahaniah had “a leadership style defined by compassion, equity, and profound humility.”

That job informed his interest in addressing the state’s primary care crisis, he said. With a shortage of primary care physicians, new patients in Boston wait an average of 40 days for an appointment, according to the Massachusetts Health Policy Commission.

“Primary care is tied to a lot of our challenges around access, around equity, around cost,” Mahaniah said. “Here in Massachusetts, most of the players are ready to consider working together to put in place something that works in terms of primary care.”

An assistant professor in the Department of Family Medicine at Tufts University School of Medicine, Mahaniah plans to continue seeing patients while serving as HHS secretary, the state’s release said. He attended medical school at Thomas Jefferson University in Philadelphia and has a master’s in business from UMass Amherst, according to the state’s news release.

Born to a father from the Democratic Republic of Congo and an American mother, Mahaniah lived in both his father’s home nation and in Switzerland as a child, he said. His father is a college professor and his mother retired last year from health care work.

Experts said the change would replace someone largely seen as coming from the hospital world with someone steeped in the needs of smaller health care providers.

“Its fair to say … there might be greater sensitivity to some of the needs of those smaller and more challenged providers,” said Paul Hattis, a senior fellow from the Lown Institute.

Walsh’s experience as a hospital administrator was a good fit for the crisis prompted by the Steward Hospital System’s bankruptcy last year, which caused the state’s health care infrastructure to teeter. Financial mismanagement of the health system’s hospitals contributed to the deaths of at least 15 patients and is still the subject of a Department of Justice investigation into fraud and corruption.

Walsh was a key player in coordinating the closure of two Steward hospitals and the sale of six others, while supporting the state’s hospitals burdened with former Steward patients.

Critics noted, though, the state ignored warning signs that the Steward system was unstable, and rescuing its surviving former hospitals cost hundreds of millions in taxpayer dollars. Walsh played a controversial role when she called Steward CEO Ralph de la Torre to encourage him to rehire a nurse whose error in judgment during a time of hospital crisis contributed to a patient’s death, the Globe reported. The nurse’s husband was a high ranking health official in the Healey administration.

Prior to serving as secretary, Walsh’s 13-year tenure at BMC, Massachusetts’ largest safety net hospital, was among the longest for hospital CEOs in the state. Under her watch BMC treated nearly two dozen people in the aftermath of the 2013 Boston Marathon bombing, an experience Walsh later said brought staff closer together.

Hattis said many understood Walsh, who was in the twilight of her career as a hospital executive, had to be convinced by Healey to take on the job as secretary of HHS. The role proved no less challenging for her than her predecessors.

Walsh’s departure comes as the Steward crisis in Massachusetts has largely abated and the intensive lobbying effort in the lead up to discussions around the federal Medicaid bill have come to an end, marking a pivotal moment in two of the state’s major health care crises.

”It doesn’t seem hard to see why this is a good time to step down in light of the federal law that will create a set of new challenges for the state,” Hattis said. “Maybe she’s been through enough already.”

Jason Laughlin can be reached at jason.laughlin@globe.com. Follow him @jasmlaughlin. Jessica Bartlett can be reached at jessica.bartlett@globe.com. Follow her @ByJessBartlett.