He had been receiving treatment for two years for cancer, his fellow editor at CounterPunch, Jeffrey St. Clair, wrote on the publication's website.
Cockburn, who lived in recent years in Petrolia, Calif., was known for an acidic pen that spared few on either the left or right for policies he felt were hypocritical or corrupt.
In his last column for The Nation, published July 11, he lamented the "culture of rabid criminality" in the international banking system and predicted that even reform and tough enforcement wouldn't save it from eventual collapse.
In another recent missive, he likened President Barack Obama to the late North Korean dictator Kim Jong Il for supporting the handling of suspected terrorists in military, rather than civilian courts -- a step he called another "mile marker in the steady slide of the U.S. downhill towards the status of a banana republic." Cockburn infuriated some liberals by writing skeptically about global warming, and bothered neoconservatives with his ferocious attacks on Israel.
"He was an extraordinarily provocative, polemical, elegant columnist and writer. And he certainly was someone who never wavered in dissenting from what was the conventional line," said Katrina vanden Heuvel, editor and publisher of The Nation.
Cockburn disclosed his illness to only a few people.
In his essay announcing Cockburn's death, St. Clair wrote that he kept quiet about the cancer because he didn't want friends and readers showering him with sympathy.
Born in Scotland in 1941 and raised in Ireland, Cockburn was the son of the British novelist Claud Cockburn. In the 1970s and '80s he wrote for the Village Voice, but was fired for taking a $10,000 grant from the Institute of Arab Studies to write a book about Israel's invasion of Lebanon. He also had a column for a time in The Wall Street Journal.
But his longest affiliation was with The Nation, where Cockburn wrote columns for decades attacking U.S. foreign policy, lambasting the mainstream press and assailing Democrats for not being progressive enough. He also became known for his battles in print with a fellow columnist at The Nation, Christopher Hitchens. He co-founded CounterPunch with St. Clair in 1996.