Lewis was a prominent New York Times columnist who championed liberal causes like free speech and human rights during his 32 years at the newspaper. His columns railed against the Vietnam War, Watergate, apartheid in South Africa and Israeli settlements in the West Bank and Gaza.
"His fearlessness, the clarity of his writing and his commitment to human rights and civil liberties are legendary," said, Gail Collins, who was the editorial page editor for the Times when Lewis resigned. "And he's also one of the kindest people I have ever known."
His first Pulitzer was won in 1955 during the McCarthyism period when he was a reporter at the age of 28. Lewis defended a Navy civilian who was falsely accused of being a communist sympathizer.
Lewis won his second Pulitzer in 1963 for his coverage of the Supreme Court.
His acclaimed 1964 book, "Gideon's Trumpet," told the story of a petty thief whose fight for legal representation led to a landmark Supreme Court decision. The book became a legal classic and was later made into a television movie starring Henry Fonda.
Lewis' final "Abroad at Home" column for The Times was published Dec. 15, 2001, warning against the U.S. fearfully surrendering its civil liberties in the wake of the Sept. 11 terrorist attack.
"The hard question is whether our commitment to law will survive the new sense of vulnerability that is with us all after Sept. 11," he wrote. "It is easy to tolerate dissent when we feel safe."
Lewis also taught at universities including Harvard, Columbia, California, Illinois, Oregon, Arizona and Stanford.
He married Margaret Marshall in 1984, who became chief justice of the Massachusetts Supreme Judicial Court in 1999. She retired in 2010 to spend more time with her husband after he was diagnosed with Parkinson's disease.
The Associated Press contributed to this report.