RELATED LINK: Get live election results HERE
Forty-two-year-old Seth Williams will be the city's first new DA in nearly 20 years.
He will succeed longtime incumbent Lynne Abraham, who did not seek another term. She has served in the post since 1991.
In the May primary, Williams defeated four other Democrats to earn his party's nomination. The little-known Mike Untermeyer was unopposed.
The victory for Williams on Tuesday comes four years after he unsuccessfully challenged Abraham, his former boss and a fellow Democrat.
Williams had the backing of several key African-American groups, some of which have criticized Abraham for her aggressive pursuit of the death penalty.