Cardozo was born in New York City, the son of Rebecca Washington (née Nathan) and Albert Jacob Cardozo. Both Cardozo's maternal grandparents, Sara Seixas and Isaac Mendes Seixas Nathan, and his paternal grandparents, Ellen Hart and Michael H. Cardozo, were Sephardi Jews of the Portuguese Jewish community affiliated with Manhattan's Congregation Shearith Israel; their families emigrated from England before the American Revolution, and were descended from Jews who left the Iberian Peninsula for Holland during the Inquisition. Cardozo family tradition held that their ancestors were Marranos from Portugal, although Cardozo's ancestry has not been firmly traced to Portugal. "Cardozo" (archaic spelling of Cardoso), "Seixas" and "Mendes" are common Portuguese surnames. Cardozo was a twin, with his sister Emily. He was a cousin of the poet Emma Lazarus. He was named for his uncle, Benjamin Nathan, a vice president of the New York Stock Exchange and the victim of a famous unsolved murder case in 1870.

Albert Cardozo was himself a judge on the Supreme Court of New York (the state's general trial court) until he was implicated in a judicial corruption scandal, sparked by the Erie Railway takeover wars, in 1868. The scandal led to the creation of the Association of the Bar of the City of New York and Albert's resignation from the bench. After leaving the court, he practiced law until his death in 1885.

Rebecca Cardozo died in 1879 when Benjamin was quite young. He was raised during much of his childhood by his sister Nell, who was 11 years older. One of his tutors was Horatio Alger. At age 15, Cardozo entered Columbia University where he was elected to Phi Beta Kappa, and then went on to Columbia Law School in 1889. Cardozo wanted to enter a profession that could materially aid himself and his siblings, but he also hoped to restore the family name, sullied by his father's actions as a judge. When Cardozo entered Columbia Law School, the program was only two years long; in the midst of his studies, however, the faculty voted to extend the program to three years. Cardozo declined to stay for an extra year, and thus left law school without a law degree. He passed the bar in 1891 and began practicing appellate law alongside his older brother. Benjamin Cardozo practiced law in New York City until 1914. In November 1913, Cardozo was narrowly elected to a 14 year term on the New York Supreme Court, taking office on January 1, 1914.

In February 1914, Cardozo was designated to the New York Court of Appeals under the Amendment of 1899, and reportedly was the first Jew to serve on the Court of Appeals. In January 1917, he was appointed to a regular seat on the Court of Appeals to fill the vacancy caused by the resignation of Samuel Seabury, and in November 1917, he was elected on the Democratic and Republican tickets to a 14 year term on the Court of Appeals. In 1926, he was elected, on both tickets again, to a 14 year term as Chief Judge. He took office on January 1, 1927, and resigned on March 7, 1932 to accept an appointment to the United States Supreme Court.

His tenure was marked by a number of original rulings, in tort and contract law in particular. This is partly due to timing; rapid industrialization was forcing courts to look anew at old common law components to adapt to new settings. In 1921, Cardozo gave the Storrs Lectures at Yale University, which were later published as The Nature of the Judicial Process, a book that remains valuable to judges today. Shortly thereafter, Cardozo became a member of the group that founded the American Law Institute, which crafted a Restatement of the Law of Torts, Contracts, and a host of other private law subjects. He wrote three other books that also became standards in the legal world.

In 1932, President Herbert Hoover appointed Cardozo to the Supreme Court of the United States to succeed Justice Oliver Wendell Holmes. The New York Times said of Cardozo's appointment that "seldom, if ever, in the history of the Court has an appointment been so universally commended." Democratic Cardozo's appointment by a Republican president has been referred to as one of the few Supreme Court appointments in history not motivated by partisanship or politics, but strictly based on the nominee's contribution to law. However, Hoover was running for re-election, eventually against Franklin Roosevelt, so a larger political calculation may have been operating.

Cardozo was confirmed by a unanimous voice vote in the Senate on February 24. On a radio broadcast on March 1, 1932, the day of Cardozo's confirmation, Clarence C. Dill, Democratic Senator for Washington, called Hoover's appointment of Cardozo "the finest act of his career as President". The entire faculty of the University of Chicago Law School had urged Hoover to nominate him, as did the deans of the law schools at Harvard, Yale, and Columbia. Justice Harlan Fiske Stone strongly urged Hoover to name Cardozo, even offering to resign to make room for him if Hoover had his heart set on someone else (Stone had in fact suggested to Calvin Coolidge that he should nominate Cardozo rather than himself back in 1925). Hoover, however, originally demurred: there were already two justices from New York, and a Jew on the court; in addition, Justice James McReynolds was a notorious anti-Semite. When the chairman of the Senate Foreign Relations Committee, William E. Borah of Idaho, added his strong support for Cardozo, however, Hoover finally bowed to the pressure.

Cardozo was a member of the Three Musketeers along with Brandeis and Stone, which was considered to be the liberal faction of the Supreme Court. In his years as an Associate Justice, he handed down opinions that stressed the necessity for the tightest adherence to the tenth amendment.

In late 1937, Cardozo had a heart attack, and in early 1938, he suffered a stroke. He died on July 9, 1938, at the age of 68 and was buried in Beth - Olam Cemetery in Queens. His death came at a time of much transition for the court, as many of the other justices died or retired during the late 1930s and early 1940s.

As an adult, Cardozo no longer practiced his faith (he identified himself as an "agnostic"), but remained proud of his Jewish heritage.

Of the six children born to Albert and Rebecca Cardozo, only Emily, his twin sister, married, and she and her husband did not have any children. As far as is known, Benjamin Cardozo led a celibate life. The fact that Cardozo was unmarried and was personally tutored by the writer Horatio Alger (who had been accused of inappropriate sexual relations with young boys) has led some of Cardozo's biographers to insinuate that Cardozo was homosexual, but no real evidence exists to corroborate this possibility. Constitutional law scholar Jeffrey Rosen noted in a New York Times Book Review of Richard Polenberg's book on Cardozo:

Andrew Kaufman, a Harvard Law School professor and Cardozo biographer, notes that "Although one cannot be absolutely certain, it seems highly likely that Cardozo lived a celibate life." Judge Learned Hand is quoted in the book as saying about Cardozo: "He [had] no trace of homosexuality anyway."

Cardozo was the second Jew, after Louis Brandeis, to be appointed to the Supreme Court.

Since Cardozo was a member of the Spanish and Portuguese Jewish community, there has been recent discussion as to whether he should be considered the 'first Hispanic justice,' a notion which is disputed. Cardozo biographer Kaufman, for example, questioned the usage of the term "Hispanic" in the justice's lifetime, stating: "Well, I think he regarded himself as a Sephardic Jew whose ancestors came from the Iberian Peninsula.” It has also been asserted that Cardozo himself "confessed in 1937 that his family preserved neither the Spanish language nor Iberian cultural traditions". Both the National Association of Latino Elected Officials and the Hispanic National Bar Association consider Sonia Sotomayor to be the first unequivocally Hispanic justice.

Cardozo's opinion of himself shows some of the same flair as his legal opinions:

In truth, I am nothing but a plodding mediocrity — please observe, a plodding mediocrity — for a mere mediocrity does not go very far, but a plodding one gets quite a distance. There is joy in that success, and a distinction can come from courage, fidelity and industry.