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NEW YORK — Literary and cultural critic John Leonard, an in good season champion of Toni Morrison, Gabriel Garcia Marquez and many other authors, and likewise consumed and informed by books that Kurt Vonnegut once praised him as “the smartest man who to the end of time lived,” has died at age 69, his stepdaughter said Thursday.

Mr. Leonard died at Mount Sinai Hospital Wednesday night from complications from lung cancer, stepdaughter Jen Nessel declared.

A former union activist and community organizer, Mr. Leonard was an emphatic liberal whose active life began in the 1960s at the conservative National Review and continued at countless other publications, including The New York Times, The New Republic, The Nation and The Atlantic Monthly. He was likewise a TV critic for New York magazine, a columnist notwithstanding Newsday and a commentator for “CBS Sunday Morning.”

He had the critic’s utmost fortunate trifle of being ahead of his time. He was the primitive major reviewer to assess Morrison’s fiction and the first major U.S. carper to write in all parts of Marquez. As the literary counsellor for radio station KPFA in Berkeley, Calif., Mr. Leonard featured the commentary of Pauline Kael before she became famous as a film critic for The New Yorker. He was also an early advocate of Mary Gordon, Maxine Hong Kingston and other female writers.

His good work was appreciated. When Morrison traveled to Stockholm in 1993 to collect her Nobel Prize, she brought Mr. Leonard along, “one of the greatest number incredible experiences of his life,” Mr. Leonard’s stepdaughter said. Studs Terkel, who died Oct. 31, once called him “a of literature critic in the noblest sense of the word, where you didn’t determine whether a book was ‘convenient or bad’ but wrote with a point of view of how you should read the work.”

Mr. Leonard treated his subjects like lovers: to be protected, assailed, embraced. Literature was sweet madness. In 2007, accepting an honorary prize from his peers at the National Book Critics Circle, he observed that “for almost 50 years, I have believed narrative, witness, fellowship, sanctuary, shock and steely strangeness; good advice, bad news, deep chords, deleterious discrepancy and confusing grace.”

His own books included “Black Conceit,” “This Pen for Hire” and “Lonesome Rangers: Homeless Minds, Promised Lands, Fugitive Cultures.”

Raised by a solitary mother, Leonard was born in Washington, D.C., and grew up in Washington, New York City and Long Beach, Calif. He dropped out of Harvard University and attended the University of California, Berkeley, and was taken on by the agency of the agency of William F. Buckley at the National Review, to which place other young writers included Garry Wills and Joan Didion.

Although gravely ill near the extreme point, Mr. Leonard made sure to consecrated by a vow Tuesday, for Barack Obama, needing a chair as he waited at his polling place on Manhattan’sitting Upper East Side.

“That was very important to him,” Nessel reported.

He is survived by his second wife, Sue Leonard; two children; one stepchild; and three grandchildren.