Constance Juanita Baker was born on September 14th, 1921 in New Haven, Connecticut. She was the ninth of twelve children of Rachel Huggins and Willoughby Alva Baker, both emigrants from Nevis, British West Indies. Her childhood neighborhood, although ethnically diverse (comprised of West Indian, Irish, Italian, Jewish, and Polish families) was relatively free from racial rancor. Rachel Baker was a founder of the New Haven NAACP and Motley was exposed to African American history, especially the writings of W.E.B. DuBois, in her Sunday School. While in high school, Motley became president of the New Haven Youth Council and was secretary of the New Haven Adult Community Council. In 1939, she graduated with honors from Hillhouse High School. Though she had already formed a desire to practice law, Motley lacked the means to attend college, and instead went to work for the National Youth Administration. She also continued her involvement in community activities and it was through this work that she encountered local businessman and philanthropist Clarence Blakeslee, who, after hearing Motley speak at a New Haven community center, offered to pay for her education. She spent a year at Fisk University in Nashville, Tennessee, then transferred to New York University in 1942, earning her A.B. in economics from its Washington Square College in 1943. In February 1944 she began her legal studies at Columbia Law School. She graduated in 1946, the same year she married Joel Wilson Motley, Jr., a real estate and insurance broker. Their son, Joel Motley III, was born in 1952.

In 1945 Constance Motley took a job as law clerk to Thurgood Marshall, chief counsel of the NAACP's Legal Defense and Educational Fund, Inc. (LDEF), and accompanied Marshall to court for most of his cases. After earning her law degree, Motley continued to work for the LDEF. In 1950 she was named assistant counsel and in 1961 she became associate counsel when Jack Greenberg succeeded Thurgood Marshall as head of the LDEF. As counsel Motley was involved in almost every important civil rights case of the era. She worked on litigation for the 1954 school desegregation case, Brown v. the Board of Education of Topeka, Kansas and subsequently fought for and won several other successful public school and university desegregation cases, including James Meredith's entry into the University of Mississippi in 1962. The LDEF also represented Dr. Martin Luther King, Jr. and his followers in civil rights campaigns for desegregation of public transportation and accommodations throughout the South from 1961 to 1963. Motley brought many of these civil rights cases to higher courts. Between 1961 and 1964, she argued ten civil rights cases before the U.S. Supreme Court, winning nine. [For a complete list and summaries of Motley's NAACP cases see the Columbia University project database, described in the Scope and Contents note]. In his book, Crusaders in the Courts (1994), Jack Greenberg said of Motley's work with the NAACP: "[She] was a dogged opponent of Southern segregationists, who found her tougher than Grant at Vicksburg. She dug in to a position and wouldn't let go in the face of all kinds of threats, evasion, obfuscation, and delay.".

In the late 1950s Motley had begun to be active in New York State politics. She served as a member of the New York State Advisory Council on Employment and Unemployment Insurance from 1958 to 1964, and in February 1964, she left the NAACP, having won a special election to the New York State Senate, becoming the first African American woman to serve in that body. As State Senator for the 21st Congressional District in Manhattan (roughly from 96th street on the upper west side to 161st street in Harlem), Motley launched a campaign during her first seven weeks in office to extend civil rights legislation in employment, education, and housing. She was re-elected to the Senate in November 1964 and served until February 1965, when New York City Council elected her the first woman to serve as President of the Borough of Manhattan. She was re-elected in the city-wide elections of November 1965 for a full four-year term and was the first candidate for the Manhattan Presidency to win the endorsement of the Republican, Democratic, and Liberal Parties. As Borough President, Motley drew up a seven-point program for the revitalization of Harlem and East Harlem, and won a pioneering fight for $700,000 to plan renewal projects for those and other underprivileged areas of the city. The plan included a design to decrease racial segregation in the public schools serving the housing projects.

In January 1966 Motley was nominated by President Lyndon B. Johnson for a judgeship in the Federal District Court for the Southern District of New York--the nation's largest federal court covering Manhattan, the Bronx, and six New York counties. Over tremendous opposition from southern senators (led by Senator James Eastland of Mississippi) and other federal judges, Motley was confirmed in August 1966, becoming the first woman to occupy that post, and the first African American woman ever named to the federal bench. Judge Motley continued to be a strong supporter of civil rights for minorities and the poor, as well as for women's rights. Among her many controversial decisions was the infamous "locker room case" Ludtke v. Kuhn (1978), in which she ruled that a woman reporter be admitted to the New York Yankees' locker room. In another highly publicized case Judge Motley admonished the New York City police for not providing Vietnam war protesters with adequate protection against violence in the streets (Belknap et al v. Leary, 1970). [These and other notable cases presided over by Judge Motley are summarized in the Columbia University project which is described in the Scope and Content note below.] In 1982, Judge Motley was appointed Chief Judge of the Southern District of New York and held senior status since 1986. Constance Baker Motley died in New York City in September 2005.