The civil rights leader addressed about 250,000 people from the steps of the Lincoln monument, the majority of them African-Americans seeking social justice and economic equality.
He delivered his speech on Aug. 28, 1963 during the March on Washington for civil rights, and the address has served as the rallying cry for racial equality in the United States ever since.
Today, about 100,000 people are expected to march from the National Mall's Lincoln Memorial to the Washington Monument, passing by the Martin Luther King Jr. Memorial.
Among the speakers at the march will be Trayvon Martin's mother, Sybrina Fulton. Travyon Martin was the unarmed African-American teenager who was shot by his aunt's neighbour George Zimmerman, a man later acquitted of murder in the case, sparking debate about race and the laws of self-defence in the U.S.
CBC's Briar Stewart is in Washington following the preparations for celebrations commemmorating King's speech and has this report.