The cause was complications of a blood infection, his family said.
Mr. Brown was most often described as a jazz singer, and he initially achieved fame by putting lyrics to well-known jazz instrumentals like Miles Davis's All Blues" and Mongo Santamaria's Afro Blue," but efforts to categorize him usually failed. As a performer, he acted his songs more than he sang them; as a songwriter, he drew as much from gospel, the blues and folk music as he did from jazz. He preferred to call himself an entertainer, although even that broad term did not go far enough: he saw his art as a way to celebrate African-American life and attack racism, and it was not always easy to tell where the entertainer ended and the activist began.
His song Brown Baby," recorded by Mahalia Jackson and others, was both a lullaby for his infant son and an anthem of racial pride. Other songs, like Signifying Monkey" and The Snake," took their story lines from black folklore. The album We Insist! Freedom Now Suite," for which Mr. Brown wrote lyrics to the drummer Max Roach's music, was one of the first jazz works to address the civil rights movement.
His commitment to art as a tool for change was most evident in the numerous stage shows he wrote and directed in his native Chicago, which addressed social issues and often had poor black teenagers in their casts. The most famous of these shows, Opportunity, Please Knock," was created in 1967 with members of the Blackstone Rangers, a street gang. His most recent production was a 2002 revival of Great Nitty Gritty," a show about gang violence that he had first staged 20 years earlier with young residents of the Cabrini Green housing project.
Oscar Brown Jr. was born in Chicago on Oct. 10, 1926. His performing career began early: he acted in radio dramas as a teenager and was the host of a local radio program called Negro Newsfront" while still in his 20's. But he did not become actively involved in music until after he had worked briefly for his father's real estate business, run unsuccessfully for public office twice, and served a two-year Army hitch.