Beckwith was 80.
Barbara Austin, a hospital spokeswoman, said Beckwith entered University Medical Center at 2:07 p.m. CDT Sunday. She could not elaborate on his ailment or the cause of death.
"It's a matter for the coroner's office to determine," she said.
Evers, a 37-year-old field secretary for the National Association for the Advancement of Colored People who pushed for an end to segregation, had stepped out of his car when he was shot in the back on June 12, 1963. He was walking to his house with an armful of "Jim Crow Must Go" T-shirts.
Beckwith, a white supremacist, was convicted at a third trial in 1994 after two mistrials three decades earlier. After his conviction, he was sentenced to life imprisonment.
His fingerprint was found on a deer rifle used to kill Evers. It was abandoned in the lot across the street. But the former fertilizer salesman insisted he was 90 miles (145 kilometers) away in Greenwood when Evers was murdered.
Two all-white juries deadlocked in trials in 1964. Twelve years ago, Evers' widow, Myrlie Evers Williams, asked for the case to be reopened, and Hinds County District Attorney Bobby DeLaughter agreed.
"At the very beginning ... we didn't have anything," DeLaughter said. "The DA's file was nowhere to be found. We did not have the benefit of a trial transcript to know who the witnesses were. None of the evidence had been retained by the court."
But DeLaughter and his officers stumbled across new evidence, including negatives from the crime scene and new witnesses who testified Beckwith had bragged to them "about beating the system."
Beckwith was arrested Dec. 17, 1990, and when he stood in front of a new jury in 1994, he was 74 years old.
His prosecutors were armed with new evidence and a 127-page document claiming 21 errors were made in Beckwith's original trial. Also, eight of the 12 jurors were black.
Beckwith was found guilty of murder and the Mississippi Supreme Court upheld the decision in 1997.
Beckwith is survived by his wife and a son.
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