After graduating from high school in 1945, Dinkins attempted to enlist in the U.S. Marine Corps but was told that the “Negro quota” had already been met. He eventually was drafted and served with the Marines. He went to Howard University on the GI Bill of Rights, studying mathematics (B.S., 1950). In 1953 Dinkins entered Brooklyn Law School and was introduced to politics when he married Joyce Burrows, the daughter of a New York state assemblyman. He joined a law firm and became increasingly involved with the Democratic Party.

Elected to a term in the state assembly in 1965, he later served as president of elections for New York City, as city clerk, and as Manhattan borough president before his successful bid for the mayor's office in 1989. Dinkins took office at a time when New York City was racked by racial discord. Both ethnic tensions and crime statistics increased during his term, and he became the first black mayor of a major U.S. city to be denied reelection.