"Hubris is a fit word for today's demolition" of the law, she said.
Reaction to the ruling from elected officials generally divided along partisan lines.
Mississippi Lt. Gov. Tate Reeves, a Republican, said in a news release, "The practice of preclearance unfairly applied to certain states should be eliminated in recognition of the progress Mississippi has made over the past 48 years."
But Democratic Rep. Bennie Thompson, the only black lawmaker in Mississippi's congressional delegation, said the ruling "guts the most critical portion of the most important civil-rights legislation of our time."
Alabama's Bentley, a Republican, pointed to his state's legislature -- 27 percent black, similar to Alabama's overall population -- as a sign of the state's progress.
The court challenge came from Shelby County, Ala., a Birmingham suburb.
The prior-approval requirement had applied to the states of Alabama, Alaska, Arizona, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia. It also covered certain counties in California, Florida, New York, North Carolina and South Dakota and some local jurisdictions in Michigan. Coverage was triggered by past discrimination not only against blacks, but also against American Indians, Asian-Americans, Alaska Natives and Hispanics.
Obama, whose historic election was a subtext in the court's consideration of the case, pledged that his administration would continue to fight discrimination in voting. "While today's decision is a setback, it doesn't represent the end of our efforts to end voting discrimination," the president said. "I am calling on Congress to pass legislation to ensure every American has equal access to the polls."
Congress essentially ignored the court's threat to upend the voting rights law in a similar case four years ago. Roberts said the "failure to act leaves us today with no choice."
Congressional Democrats said they are eager to make changes, but Republicans were largely noncommittal.
Sen. Charles Schumer, D-N.Y., said he expects Republicans to block efforts to revive the law, even though a Republican-led Congress overwhelmingly approved its latest renewal in 2006 and President George W. Bush signed it into law.
"As long as Republicans have a majority in the House and Democrats don't have 60 votes in the Senate, there will be no preclearance. It is confounding that after decades of progress on voting rights, which have become part of the American fabric, the Supreme Court would tear it asunder," Schumer said.