De Priest was born in Florence, Alabama to former slaves. His mother worked part-time as a laundress, and his father, Alexander, was a teamster associated with the "Exodus" movement, which arose after the American Civil War to help blacks escape continued oppression in the South by moving to other states that offered greater freedom. In 1878, the De Priests left for Dayton, Ohio, after the elder De Priest had to save a friend who was a former Congressman from a lynch mob and another black man was killed on their doorstep.
In Salina, Kansas, De Priest studied bookkeeping at the Salina Normal School. In 1889, he moved to Chicago, Illinois, where he worked as an apprentice plasterer, house painter, and decorator, and eventually became a successful contractor and real estate broker. He went on to build a fortune in the stock market and in real estate by helping black families move into formerly all-white neighborhoods. From 1904 to 1908, he was a member of the board of commissioners of Cook County, Illinois, and he then served on the Chicago City Council from 1915 to 1917 as alderman of the 2nd Ward, Chicago’s first black alderman.
De Priest stepped down as alderman in 1917 after being indicted for alleged involvement with Chicago's South Side black mob, but was acquitted after hiring Clarence Darrow to defend him.
In 1919, De Priest ran unsuccessfully for alderman as a member of the People's Movement Club, a political organization he founded. However, after a few years, De Priest's organization became the most powerful of Chicago's many black political organizations, and he became the top black politician under Chicago Republican mayor William Hale Thompson.
In 1928, when Republican congressman Martin B. Madden died, Mayor Thompson selected De Priest to replace him on the ballot and he became the first African American elected to Congress in the 20th century, representing the 1st Congressional District of Illinois (the Loop and part of the South Side of Chicago) as a Republican. During his three consecutive terms (1929–1935) as the only black representative in Congress, De Priest introduced several anti-discrimination bills. His 1933 amendment barring discrimination in the Civilian Conservation Corps (CCC) was passed by the Senate and signed into law by President Franklin D. Roosevelt. A second bill, an anti-lynching bill, failed, even though it would not have made lynching a federal crime. A third proposal, a bill to permit a transfer of jurisdiction if a defendant believed he or she could not get a fair trial because of race or religion, was passed by a later Congress.
Civil rights activists criticized De Priest for opposing federal aid to the poor, but they applauded him for speaking in the South despite death threats. They also praised De Priest for telling an Alabama senator he was not big enough to prevent him from dining in the Senate restaurant, and for defending the right of Howard University students to eat in the House restaurant. De Priest took the House restaurant issue to a special bipartisan House committee. In a three month-long heated debate, the Republican minority argued that the restaurant's discriminatory practice violated 14th Amendment rights to equal access. The Democratic majority skirted the issue by claiming that the restaurant was not open to the public, and the House restaurant remained segregated.
In 1929, De Priest made national news when first lady Lou Hoover, at De Priest's urging, invited his wife, Jessie Williams De Priest, to a tea for congressional wives at the White House. De Priest also appointed Benjamin O. Davis, Jr., to the United States Military Academy at a time when the army had only one African-American line officer (Davis's father, Benjamin O. Davis, Sr.).
By the early 1930s, De Priest's popularity waned because he continued to oppose higher taxes on the rich and fought Depression-era federal relief programs. De Priest was defeated in 1934 by Democrat Arthur W. Mitchell, who was also an African American. He was again elected to the Chicago City Council in 1943 as alderman of the 3rd Ward, and served until 1947. He died in Chicago at age 80 and is buried in Graceland Cemetery.
Oscar married the former Jessie L. Williams (1873?-March 31, 1961). This union had two sons:
- Laurence W. (1900? - July 28, 1916)
- Oscar Stanton De Priest, Jr. (May 24, 1906-November 8, 1983)
Before Oscar DePriest, the Republican Representative from Chicago's First District, was sworn in on April 15, he was accused of election fraud and had difficulty in obtaining office space. The charges of fraud were unsupported and New York Representative Fiorello H. LaGuardia offered the office next to his to DePriest. DePriest was the first African American elected to Congress in the twentieth century, the first African American Congressperson since 1901 and the first African American to be elected to Congress from a Northern state.
Mrs. DePriest's attendance at the official White House Congressional tea became a national cause celebre. The Florida House of Representatives adopted a resolution condemning "certain social policies of the Administration in entertaining Negroes in the White House on a parity with white ladies." Senator Blease of South Carolina introduced a resolution to the effect that President and Mrs. Hoover should "remember that the house in which they are temporarily residing is the "White House," and that Virginia, Texas, Florida, Tennessee and North Carolina contributed to their becoming its custodians."
After his election to Congress, DePriest was constantly in demand as a speaker. He did realize that he was not only a representative of voters from Illinois 1st Congressional District, but also a symbol for black people. He urged his many audiences to study political organization to learn their rights under the Federal Constitution, and to see campaign activity as a public duty.
A native son of Florence, Alabama, DePriest's early interest in politics can be traced back to his father, Alexander DePriest, who knew and admired James T. Rapier, an African American who represented Alabama in Congress in the days of Reconstruction. The elder DePriest learned to study people and politics while a dray man; Oscar DePriest learned them through his successful career as a real estate entrepreneur. Through his long life he maintained a keen interest in politics and in the progress of blacks. His success in business and politics did not change him, he insisted to his dying day in 1951 that "I am of the common herd".