In a 5-4 ruling, the sharply divided high court struck down a key component of the 1965 Voting Rights Act.
The court upheld the part of the law that forced jurisdictions with a history of racial discrimination to seek permission of the federal government when they change election procedures.
But the high court invalidated the way those jurisdictions are mapped out and left it up to a bitterly polarized Congress to decide how, or whether, to come up with a new formula.
This decision by the court today is a game changer and leaves virtually unprotected minority voters in communities all over this country," said Sherrilyn Ifill, President of the Legal Defense Fund.
The law covered nine states and parts of six others.
Shelby County, Alabama successfully argued that it, and the nation, have come a long way since the 1960s with African-Americans holding prominent positions from local government all the way up to the White House.
In a 5-4 decision written by Chief Justice John Roberts, The court found that the country had changed.
But dissenting Justice Ruth Bader Ginsburg said the country had changed because of the law.
The court finishes its session tomorrow with decisions on two same-sex marriage cases that are among the most anticipated decisions in years.