Born in New Britain, Connecticut to a Jewish family, he attended public schools and New York University. He graduated from the University of Chicago Law School in 1933 and was admitted to the bar the same year.

He began his political career as a member of the Connecticut state legislature, serving in that body from 1938 to 1942. From 1941 until 1943 and again from 1945 to 1947 he was judge of Hartford Police Court.

He was elected as a Democrat to the 81st and 82nd Congresses serving from 1949 until 1953. In 1952 he had an unsuccessful bid for election to fill a vacancy in the United States Senate, losing to Prescott Bush.

From 1955 to 1961 he was Governor of Connecticut, serving until he was sworn in as Secretary of the Department of Health, Education, and Welfare in JFK's Presidential Cabinet. He was finally elected to the United States Senate in 1962 and served in the Senate from January 3, 1963, until January 3, 1981.

At the 1968 Democratic National Convention, during a speech nominating George McGovern, he went off-script, saying, "If George McGovern were president, we wouldn’t have these Gestapo tactics in the streets of Chicago." Many conventioneers, having been appalled by the response of the Chicago police to the simultaneously occurring anti-war demonstrations, promptly broke into ecstatic applause. As television cameras focused on an indignant Chicago Mayor Richard J. Daley, lip-readers throughout America claimed to have observed him shouting, "Fuck you, you Jew motherfucker." Defenders of the mayor would later claim that he was calling Senator Ribicoff a faker.

In 1972, after the withdrawal of Senator Thomas Eagleton from the Democratic vice-presidential nomination, presidential nominee George McGovern asked Senator Ribicoff (among others) to take Eagleton's place. Ribicoff refused, and McGovern eventually chose Sargent Shriver as his running mate.

During his time in the Senate he was chairman of the U.S. Senate Committee on Government Operations (94th and 95th Congresses) and its successor committee, the U.S. Senate Committee on Governmental Affairs (95th and 96th Congresses).

In 1981, he retired from the Senate and took a position as special counsel in the New York law firm of Kaye Scholer LLP and resided in Cornwall Bridge, Connecticut.

He died in New York City in 1998 and is buried at Cornwall Cemetery.

This article incorporates facts obtained from the public domain Biographical Directory of the United States Congress.