On an unseasonably warm night in February, dinner guests at Gen. Mark A. Milley’s Virginia home were wondering, a bit nervously, what could possibly be going on.

General Milley, the chairman of the Joint Chiefs of Staff, had been called away once, twice, three times, retreating upstairs to a secure room to consult with other top military brass. His wife, Hollyanne, was also missing.

A Chinese spy balloon had been detected over the Western United States. Soon, President Biden was on the line with General Milley, his highest-ranking military official, unbeknown to the guests downstairs. And Mrs. Milley, a nurse of nearly four decades, was busy making calls from another room upstairs, oblivious to the drama unfolding next door.

“I was on the phone with patients,” Mrs. Milley recalled about the evening, “so I couldn’t come down.”

That parallel commitment to their work has persisted through the chairman’s dramatic four-year term, set to end on Saturday, during which the Milleys have navigated a global pandemic, the chaotic withdrawal of American troops from Afghanistan and repeated attacks from former President Donald J. Trump. Without saying so, the couple, interviewed at their dining room table in Arlington, leave the impression that the term is ending not a moment too soon.

Mrs. Milley, 58, has worked almost everywhere her husband has been stationed, although she did not accompany him on deployments. A list of more than 20 stops and deployments is enshrined in their home with a stack of placards nearly as tall as the door it is next to. She is one of just a few spouses of a Joint Chiefs chairman to have maintained an accomplished career of her own. And as the chairman prepares to retire, Mrs. Milley has no intention of slowing down, with plans to return to the field as a Red Cross disaster volunteer.

“Her saying to me is, ‘You’ve been deploying all our life,’” General Milley said. “‘Now you’re going to be staying home and I’m deploying.’”

“I have the skills, and our children are grown, and I have the time,” Mrs. Milley added.

Mrs. Milley carries a C.P.R. mask wherever she goes, and has jumped into action at more than one official event. Her most famous impromptu rescue came on Veterans Day in 2020, at the Tomb of the Unknowns in Arlington National Cemetery.

“I saw this gentleman, he just looked weak walking up” to the memorial, Mrs. Milley said. In the seconds she took her eyes off him, he fell to the ground, unresponsive.

She quickly began chest compressions, possibly saving his life, minutes before Mr. Trump and Vice President Mike Pence arrived.

“She absolutely cringes at the mere thought of having to speak publicly,” said Rosemary Williams, a former official in the Department of Veterans Affairs and a close friend of the couple. “This changes when there’s someone in front of her who is ill or injured. Suddenly, she’s out front, she’s elbowing people aside, she’s giving orders.”

Mrs. Milley is known for handing out homemade cookies to military families she meets while traveling overseas with her husband. But the reality of their past four years in Washington has often been more burdensome, and some people close to Mrs. Milley say the experience has been very hard on her at times.

June 1, 2020, may have been the lowest point of General Milley’s tenure. Wearing military fatigues, he marched behind Mr. Trump and his advisers from the White House across nearby Lafayette Square to stage a photo in front of St. John’s Church, after Park Police used tear gas to clear Black Lives Matter protesters in the park.

General Milley realized too late that he had helped create a perception that the military had endorsed Mr. Trump’s stunt, he later said.

“He talked a lot about it,” Mrs. Milley said. “It was difficult personally. It was difficult to watch the media unfold, and how it affected our children, our extended family.”

General Milley drafted a resignation letter a week later, telling Mr. Trump that he was doing “irreparable harm” and “ruining the international order,” but he was counseled to stay on at the Pentagon. He apologized in a video soon afterward, saying that “I should not have been there” and calling the incident “a mistake that I have learned from.”

Mrs. Milley knew he had drafted the letter, but she said she did not read it and would have been “behind whatever decision he made.”

“I think he went through the pros and cons; I think he fell back on his beliefs,” she said.

“I’m glad he did not resign,” she added.

The tumult of that time was not unusual for the couple. Relocation has been a constant throughout Mrs. Milley’s career, but she believes living in different places has made her a stronger nurse. While at Fort Polk in Louisiana, she learned how to administer antivenin after a snakebite. At Fort Drum, a few miles south of the Canadian border in New York, she mastered cold-weather injuries, a threat she had not encountered growing up in Atlanta.

As her husband rose in rank, she devoted more time to ensuring that families of deceased service members had the resources to recover: food, child care, a robust support network. As her influence rose, Mrs. Milley began lobbying on behalf of military families to address issues both local and systemic.

“That’s how we get through day to day sometimes,” Mrs. Milley said. “I think of these families who are so frustrated, sometimes they are thinking of getting out. If we can listen to those personal challenges, that plays into retention.”

Mrs. Milley is still active in groups that assist wounded veterans and their families. And she has close ties to many around the country.

“She’s the first lady of our American military, and yet you would think she’s just a friend,” said Bonnie Carroll, the founder of the nonprofit Tragedy Assistance Program for Survivors.

One such case is Capt. Luis Avila, who spent 40 days in a coma and was left almost fully paralyzed after his vehicle hit an explosive device in Afghanistan in 2011. He sang “God Bless America” at General Milley’s swearing-in, and is set to sing the national anthem at his retirement ceremony. His wife, Claudia, calls Mrs. Milley a “mentor” and an “angel” for her humility in advocating on behalf of families like hers.

“She never told nobody who she was,” Ms. Avila said about Mrs. Milley’s visits to Walter Reed, the military medical center. “You always used to be by yourself. But she never came alone. She came with cookies.”

Mrs. Milley credits her mother, Margaret, who earned her own nursing degree after being treated for breast cancer in her 30s, with inspiring her to become a nurse. When Margaret was diagnosed, a 15-year-old Hollyanne Haas became her mother’s primary caregiver and helped raise her younger sister. Her mother’s cancer recurred at 49, and she died a year later.

Hollyanne met Mark in Key West, Fla., four decades ago and they married two years later, in 1985. The couple have a son and a daughter and three grandchildren. As this stage of their lives draws to a close, their regrets include not getting out enough around Washington and not staying as close as they would like with many of the friends they have met throughout their careers.

“I do regret we didn’t have more time as a family with all those deployments,” Mrs. Milley said. “But we will make up for that in 45 days.”

Asked if she was keeping a countdown until her husband’s retirement, she laughed and turned toward him.

“He keeps the countdown,” she said.