The 1965 Voting Rights Act (VRA) fundamentally changed the distribution of electoral power in the US South. We examine the consequences of this mass enfranchisement of Black people for the use of the carceral state—police, the courts, and the prison system. We study the extent to which white communities in the US South responded to the end of Jim Crow by increasing the incarceration of Black people. We test this with new historical data on state and county prison intake data by race (~1940–1985) in a series of difference-in-differences designs. We find that states covered by Section 5 of the VRA experienced a differential increase in Black prison admissions relative to those that were not covered and that incarceration varied systematically in proportion to the electoral threat posed by Black voters. Our findings indicate the potentially perverse consequences of enfranchisement when establishment power seeks—and finds—other outlets of social and political control.