In the 18 years since her family left their home in New Jersey and stepped into some of the most rarefied circles in Washington, Martha-Ann Alito has never sought or cultivated a particularly public identity.

As the wife of Justice Samuel A. Alito Jr., Mrs. Alito has described keeping a largely private life since his confirmation to the Supreme Court in 2006 — one grounded by raising two children and standing in support of her husband through scrutiny and sharp-elbowed politics.

On the handful of occasions she has stepped forward to address an audience or converse with reporters, Mrs. Alito has often spoken about herself in terms of her role within a tight-knit nuclear family, holding it together through her husband’s meteoric, and at times trying, rise within the judiciary.

“The most amazing part is, why do people care about our life,” she said in a 2006 interview, looking back on Justice Alito’s confirmation hearing, which at one point left her in tears and stirred discussion about the toll partisanship can take on nominees’ relatives.

But since reporting by The New York Times raised questions about how and why an upside-down American flag appeared outside her family’s home in Alexandria, Va., just days after rioters at the Capitol carried the same flag on Jan. 6, 2021, Mrs. Alito, 70, has abruptly found herself at the center of controversy. Her husband said she had placed it there amid a neighborhood spat.

By the time the family was on the cusp of moving to Washington, the Alitos’ children were college age. Mrs. Alito described welcoming the change, having left a career as a librarian to be a full-time homemaker and mother.

But the arduous preparations and the harsh reception Justice Alito encountered in Congress left a bitter memory that Mrs. Alito would recall publicly for years afterward, denouncing the proceedings and the media coverage around it.

“For me personally, the two months preceding were the horrible part of our life,” she said in remarks introducing her husband at an awards ceremony in April 2007. “And fortunately, I was not in Washington, so I did not have to read the papers or look at the blogs or look at the computer, and I have continued that standard — I no longer read except when I choose to pick up a book.”

The pointed questions Justice Alito faced from Democrats about his views on abortion, his affiliation with a conservative Princeton alumni group and whether he would defer to the court’s precedents struck Mrs. Alito as debasing.

“The way the world is these days, Sam is by far not even close to being an imminent threat to civil liberties,” she said in the 2006 interview.

Overcoming that sharp transition mirrored the upheavals of her childhood, which Mrs. Alito has discussed publicly. Her father, who worked as an air traffic controller in the Air Force, regularly moved the family between outposts in Texas, Florida, Maine and the Azores islands of Portugal. Her mother worked as a librarian on the bases where they lived.

After following her mother’s path to become a librarian for a New Jersey public library, the U.S. attorney’s office in Newark and the Justice Department, Mrs. Alito built a limited public life in Washington that has mainly centered on apolitical projects and charity work.

When Justice Ruth Bader Ginsburg’s husband, Martin Ginsburg, died in 2010, Mrs. Alito organized the publication of a cookbook as a celebration of his culinary passions. In honor of her father’s service, she has also spoken about her work as the director of a group focused on ending homelessness among veterans.

While some partners of other Supreme Court justices — such as Jane Sullivan Roberts or Virginia Thomas — have become ensnared in controversy in recent years over their professional lives and political leanings, Mrs. Alito has not.

Only in rare moments have Mrs. Alito’s personal dealings drawn attention at all: once, after she and Justice Alito shared a meal with a couple who later claimed they had been told the decision of a pending case in advance, and again when stocks and mineral interests she inherited from her father raised minor concerns about conflicts of interest in cases her husband could decide.

Mrs. Alito graduated from the University of Kentucky with a bachelor’s degree in comparative literature in 1976 and a master’s in library sciences in 1977. She met Justice Alito in the law library when he was an assistant U.S. attorney. The two were married in 1985, five years after their first date, in the church in which he was baptized.