Rehnquist's death opens a rare second vacancy on the nation's highest court and gives President Bush, whose election Rehnquist helped decide, an opportunity shape the makeup of the court for years to come.
"The Chief Justice battled thyroid cancer since being diagnosed last October and continued to perform his duties on the court until a precipitous decline in his health the last couple of days," court spokeswoman Kathy Arberg said in announcing his death.
Rehnquist was surrounded by his three children when he died at his home in suburban Arlington, Va. His wife died in 1991.
Rehnquist was appointed to the Supreme Court as an associate justice in 1971 by President Nixon and took his seat on Jan. 7, 1972. He was elevated to chief justice by President Reagan in 1986.
The death leaves Bush with his second court opening within four months and sets up what's expected to be an even more bruising Senate confirmation battle than that of John Roberts.
It was not immediately clear what impact Rehnquist's death would have on confirmation hearings for Roberts, scheduled to begin Tuesday.
The last time there were simultaneous vacancies at the court was 1971, when Justices Hugo Black and John Marshall Harlan retired in September, about a week apart. Rehnquist, then a Justice Department lawyer, urged the Nixon administration to move fast in replacing them and wound up being appointed to Harlan's seat himself.
Rehnquist presided over Clinton's impeachment trial in 1999, helped settle the 2000 presidential election in Bush's favor, and fashioned decisions over the years that diluted the powers of the federal government while strengthening those of the states.
Arberg said plans regarding funeral arrangements would be forthcoming.
Bush was notified of Rehnquist's death shortly before 11 p.m. EDT.
"President Bush and Mrs. Bush are deeply saddened by the news," said White House counselor Dan Bartlett. "It's a tremendous loss for our nation." The president was expected to make a personal statement about Rehnquist on Sunday.
Many court watchers had expected the ailing chief justice to step down over the summer, which would have given the Senate a chance to confirm his successor while the court was out of session. Instead Justice Sandra Day O'Connor announced her retirement to spend time with her ill husband. Bush chose Roberts, a former Rehnquist clerk and friend, to replace O'Connor.
Rehnquist said on July 14 he would remain on the bench as long as his health allowed.
The president could elevate to chief justice one of the court's conservatives, such as Antonin Scalia or Clarence Thomas, but it's more likely he will choose someone from outside the court.
Possible replacements include Attorney General Alberto R. Gonzales and federal courts of appeals judges J. Michael Luttig, Edith Clement, Samuel A. Alito Jr., Michael McConnell, Emilio Garza, and James Harvie Wilkinson III. Others mentioned are former Solicitor General Theodore Olson, lawyer Miguel Estrada and former deputy attorney general Larry Thompson.
Rehnquist could be an enigmatic man. Stern and cold on the bench, he had a deep throaty laugh and warm side away from it.
In his courtroom is was not uncommon for the chief judge to snap at lawyers who exceeded their time. Behind large glasses he would peer down from the bench, sometimes raising his eyebrows to an exaggerated arch at their responses.
But when he set aside his court robes, Rehnquist emerged as a family man and beloved boss who remembered even the tiniest of details about those who worked for him in his many years at the Supreme Court.
He was a lifelong sports fan, trivia buff and a student of history who spoke often to local historical societies.
Rehnquist, who loved to play tennis well into his 70s, announced last October that he had thyroid cancer. He had a trachea tube inserted to help him breathe and underwent radiation and chemotherapy treatments. He appeared frail at Bush's inauguration in January and missed five months of court sessions before returning to the bench in March.
On the court's final meeting day of the last term, June 27, Rehnquist appeared gaunt and had difficulty as he announced the last decision of the term - an opinion he wrote upholding a Ten Commandments display in Texas. His breathing was labored, and he kept the explanation short.
He had no public appearances over the summer, although he was filmed by television crews in July as he left the hospital following two nights for treatment of a fever.
Rehnquist had an extraordinary career, with many historic milestones.
In 1999, he presided over Clinton's impeachment trial from the presiding officer's chair seat in the Senate, something only one other chief justice had done. A year later he was one of five Republican-nominated justices who voted to stop presidential ballot recounts in Florida, effectively deciding the election for Bush over Democrat Al Gore.