The Supreme Court on Tuesday struck down President Trump’s executive order limiting birthright citizenship, reaffirming the long-held principle that the Constitution guarantees that nearly all children born on U.S. soil are citizens.

The ruling, which was 6 to 3 to strike down the president’s executive order, was a severe blow to a policy pursued by Mr. Trump for more than a decade, to prevent babies born to undocumented immigrants and temporary foreign residents from automatically becoming Americans.

Chief Justice John G. Roberts Jr., writing for the majority, explained that Mr. Trump’s executive order violated a right enshrined in the 14th Amendment of the Constitution. Children born in the United States to undocumented parents or to parents temporarily in the country, he wrote, are citizens at birth.

“Citizenship, then and now, was the right to have rights — to freely participate in our political community,” Chief Justice Roberts wrote. “The framers of the 14th Amendment extended that promise to ‘every free-born person in this land.’”

He added: “We keep that promise today.”

The chief justice was joined in upholding birthright citizenship by the court’s three liberal justices, along with two fellow conservatives, Justices Amy Coney Barrett and Brett M. Kavanaugh. Justice Kavanaugh wrote that he would strike down the executive order based on federal law, not the Constitution.

Mr. Trump followed the case closely, even attending part of the oral arguments in person in April. He was the first sitting president to attend an argument.

In a social media post after the ruling, the president called the Supreme Court’s decision “too bad for our Country.” He then asserted that he could “easily make it up in Congress through Legislation,” and that “no long and unwieldy Constitutional Amendment is necessary.” He urged Congress to start immediately to “work on ending expensive and unfair to our Country, Birthright Citizenship.”

Those assertions appeared at odds with the court’s ruling, given that five justices — a majority of the court — ruled that the Constitution guarantees birthright citizenship. Any measure, whether proposed as a bill or a constitutional amendment, would face long-shot odds.

The key text of the 14th Amendment reads: “All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside.”

That language, dating to the 1860s, has long been understood to grant birthright citizenship.

Chief Justice Roberts traced the underpinnings of the concept back to England, writing that colonists who crossed the Atlantic Ocean brought with them the “common law of citizenship” by birthright.

The idea that citizenship is automatically given to babies born on U.S. soil took on “particular importance” in “a nation of immigrants,” the chief justice wrote, nodding to the “tens of thousands of émigrés from the Old World — Scotch-Irish, French, German, Welsh, and many more” who arrived on American shores, “some of whom hoped to stay only a short time, others of whom hoped never to leave.”

The court had already confirmed the principle of birthright citizenship in the landmark 1898 ruling in United States v. Wong Kim Ark, Justice Roberts wrote. In that case, the court held that the 14th Amendment guaranteed citizenship to Wong Kim Ark, who was born in San Francisco to parents who were both Chinese citizens, because he was born on U.S. soil.

Three of the court’s conservatives — Justice Clarence Thomas, Justices Samuel A. Alito Jr. and Neil M. Gorsuch — dissented. Neither Justice Alito nor Justice Gorsuch was on the bench on Tuesday, the court’s final opinion day of the term.

In his 91-page dissent, joined by Justice Gorsuch, Justice Thomas said that the 14th Amendment was intended to enshrine citizenship for formerly enslaved people and their descendants, a repudiation of the court’s infamous Dred Scott case that had denied citizenship to Black people.

“Blacks were entitled to citizenship because they were Americans,” Justice Thomas wrote. “They had no other homeland, owed no allegiance to any foreign power, and were subject to no other authority.”

Justice Thomas added that “the same could not be said for the children of foreign temporary visitors,” who were “attached to their home country,” lacked “similar bonds to this country,” and “would not be called upon in time of war.”

Justice Alito called the decision “a serious mistake,” writing that the court’s view of the Constitution “confers citizenship on virtually everyone who happens to be born in this country, including the children of ‘birth tourists,’” people he characterized as “women who come here solely for the purpose of giving birth to a child and then promptly return home.”

The legal battle over birthright citizenship began on the first day of Mr. Trump’s second term, when he announced an executive order titled “Protecting the Meaning and Value of American Citizenship.”

In the order, he declared that citizenship would no longer be automatically granted to babies born on U.S. soil. In particular, children born to immigrants who entered the country illegally would no longer be citizens, nor would those born to parents here on a lawful but temporary basis, such as those on student, work or tourist visas.

The president’s order faced immediate legal challenges, as civil rights organizations, immigrant advocacy groups and expectant parents sued, successfully winning in court to block the order while lawsuits unfolded.

It never went into effect, and there were few signs the administration had been preparing the dramatic overhaul of the citizenship system that would have been necessary were it allowed.

In addition to the Constitution, the challengers also said the order violated federal statutes from 1940 and 1952, when Congress codified the language of the citizenship clause into law.

The case heard by the Supreme Court was filed in New Hampshire on behalf of two babies subject to the president’s executive order, their parents and a pregnant woman.

The Trump administration had asserted the president’s executive order “restores the original meaning of the citizenship clause.” Lawyers for the administration also said the order would affect only babies born after the order went into effect, trying to assuage concerns of millions of Americans who feared the order could cause them to lose their national identity.

Mr. Trump also drew attention to babies born through what he has called “birth tourism,” when wealthy foreigners visit the United States intending to give birth while in the country so their babies are citizens.

After Tuesday’s ruling, Cecillia Wang, the national legal director for the American Civil Liberties Union, which represented the challengers, celebrated the ruling, writing that the decision “reaffirms a fundamental American promise — if you are born here, you are a citizen.”

“A president cannot change the Constitution by executive fiat,” she wrote in an emailed statement, adding: “The Constitution’s guarantee of birthright citizenship stands strong.”

Erica L. Green, Amy Qin and Aishvarya Kavi contributed reporting.