Ellsberg was born in Chicago, Illinois, in 1931 to Jewish parents. He grew up in Detroit, Michigan, and attended Cranbrook School. His mother had wished him to be a concert pianist but he stopped playing in July 1946 when she was killed, together with his sister, after his father fell asleep at the wheel of the car the family was travelling in and crashed into a culvert wall.

Ellsberg attended Harvard University on a scholarship, graduating with B.S. in economics in 1952 (summa cum laude). He then studied at Cambridge University on a Woodrow Wilson Fellowship and one year later he returned to Harvard for graduate school. In 1954, he left Harvard for the U.S. Marine Corps. He graduated first in a class of almost 1,100 lieutenants at the Marine Corps Basic School in Quantico, Virginia. He served as a platoon leader and company commander in the Marine 2nd Infantry Division, and after satisfying his two year Reserve Officer commitment was discharged from the Corps as a first lieutenant in 1957. He resumed graduate studies at Harvard, but after two years he interrupted his academic studies again, to work at RAND, where he concentrated on nuclear strategy. He earned a Ph.D. in Economics from Harvard in 1962. His dissertation introduced a paradox in decision theory now known as the Ellsberg paradox.

Ellsberg served in the Pentagon from August 1964 under Secretary of Defense Robert McNamara (and, in fact, was on duty on the evening of the Gulf of Tonkin incident, reporting the incident to McNamara). He then served for two years in Vietnam working for General Edward Lansdale as a civilian in the State Department.

After serving in Vietnam, Ellsberg resumed working at RAND. In 1967, he contributed to a top-secret study of classified documents regarding the conduct of the Vietnam War that had been commissioned by Defense Secretary McNamara.These documents, completed in 1968, later became known collectively as the Pentagon Papers. It was because Ellsberg held an extremely high-level security clearance and desired to create a further synthesis from this research effort that he was one of very few individuals who had access to the complete set of documents.

By 1969 Ellsberg began attending anti-war events while still remaining in his position at RAND. He experienced an epiphany attending a War Resisters League conference at Haverford College in August 1969, listening to a speech given by a draft resister named Randy Kehler, who said he was "very excited" that he would soon be able to join his friends in prison.Ellsberg described his reaction:

Decades later, reflecting on Kehler's decision, Ellsberg said,

Randy Kehler never thought his going to prison would end the war. If I hadn't met Randy Kehler it wouldn't have occurred to me to copy [the Pentagon Papers]. His actions spoke to me as no mere words would have done. He put the right question in my mind at the right time.

In late 1969...with the assistance of his former RAND Corporation colleague, Anthony Russo...Ellsberg secretly made several sets of photocopies of the classified documents to which he had access; these later became known as the Pentagon Papers. As an editor of the New York Times was to write much later, these documents "demonstrated, among other things, that the Johnson Administration had systematically lied, not only to the public but also to Congress, about a subject of transcendent national interest and significance".They revealed that the government had knowledge, early on, that the war would not likely be won, and that continuing the war would lead to many times more casualties than was ever admitted publicly. Further, the papers showed the government had lied to Congress and the public.

Shortly after Ellsberg copied the documents, he resolved to meet some of the people who had influenced both his change of heart on the war and his decision to act. One of them was Kehler. Another was the poet Gary Snyder, whom he'd met in Kyoto in 1960, and with whom he'd argued about U.S. foreign policy; Ellsberg was finally prepared to concede that Snyder had been right, about both the situation and the need for action against it.

Throughout 1970, Ellsberg covertly attempted to persuade a few sympathetic U.S. Senators...among them J. William Fulbright, chair of the Senate Foreign Relations Committee, and George McGovern, a leading opponent of the war...to release the papers on the Senate floor, because a Senator could not be prosecuted for anything he said on-the-record before the Senate. Ellsberg told U.S. Senators that they should be prepared to go to jail in order to end the Vietnam War.

Ellsberg allowed some copies of the documents to circulate privately, including among scholars at the Institute for Policy Studies (IPS). Ellsberg also shared the documents with New York Times correspondent Neil Sheehan under a pledge of confidentiality. Sheehan broke his promise to Ellsberg, and built a scoop around what he'd received both directly from Ellsberg and from contacts at IPS.

On Sunday, June 13, 1971, the Times published the first of nine excerpts and commentaries on the 7,000 page collection. For 15 days, the Times was prevented from publishing its articles by court order requested by the Nixon administration. Meanwhile, Ellsberg leaked the documents to The Washington Post and 17 other newspapers. On June 30, the Supreme Court ordered publication of the Times to resume freely (New York Times Co. v. United States). Although the Times did not reveal Ellsberg as their source, he went into hiding for 13 days afterwards, suspecting that the evidence would point to him as the source of the unauthorized release of the study.

On June 29, 1971, U.S. Senator Mike Gravel of Alaska entered 4,100 pages of the Papers into the record of his Subcommittee on Public Buildings and Grounds...pages which he had received from Ellsberg via Ben Bagdikian...then an editor at the Washington Post. These portions of the Papers were subsequently published by Beacon Press.

Fallout

The release of these papers was politically embarrassing to not only those involved in the Johnson and Kennedy administrations but also the incumbent Nixon administration. Nixon's Oval Office tape from June 14, 1972, shows H. R. Haldeman describing the situation to Nixon:

[then cabinet-member Donald] Rumsfeld was making this point this morning. To the ordinary guy, all this is a bunch of gobbledygook. But out of the gobbledygook comes a very clear thing. ... It shows that people do things the president wants to do even though it's wrong, and the president can be wrong.

John Mitchell, Nixon's Attorney General, almost immediately issued a telegram to the Times ordering that it halt publication. The Times refused, and the government brought suit against it.

Although the Times eventually won the trial before the Supreme Court, an appellate court ordered that the Times temporarily halt further publication. This was the first successful attempt by the federal government to restrain the publication of a major newspaper since the presidency of Abraham Lincoln during the US Civil War. Ellsberg released the Pentagon Papers to 17 other newspapers in rapid succession. The right of the press to publish the papers was upheld in New York Times Co. v. United States.

As a response to the leaks, the Nixon administration began a campaign against further leaks and against Ellsberg personally. Aides Egil Krogh and David Young under John Ehrlichman's supervision created the "White House Plumbers", which would later lead to the Watergate burglaries.

In August 1971, Krogh and Young met with G. Gordon Liddy and E. Howard Hunt in a basement office in the Old Executive Office Building. Hunt and Liddy recommended a "covert operation" to get a "mother lode" of information about Ellsberg's mental state in order to discredit him. Krogh and Young sent a memo to Ehrlichman seeking his approval for a "covert operation [to] be undertaken to examine all of the medical files still held by Ellsberg’s psychiatrist." Ehrlichman approved under the condition that it be "done under your assurance that it is not traceable."

On September 3, 1971, the burglary of Lewis Fielding's office...titled "Hunt/Liddy Special Project No.1" in Ehrlichman's notes...was carried out by Hunt, Liddy and CIA agents Eugenio Martinez, Felipe de Diego and Bernard Barker. The "Plumbers" failed to find Ellsberg's file. Hunt and Liddy subsequently planned to break into Fielding's home, but Ehrlichman did not approve the second burglary.

The break-in was not known to Ellsberg or to the public until it came to light during Ellsberg and Russo's trial in April 1973.

On June 28, 1971, two days before a Supreme Court ruling saying that a federal judge had ruled incorrectly about the right of the New York Times to publish the Pentagon Papers, Ellsberg publicly surrendered to the United States Attorney's Office for the District of Massachusetts in Boston. In admitting to giving the documents to the press, Ellsberg said:

I felt that as an American citizen, as a responsible citizen, I could no longer cooperate in concealing this information from the American public. I did this clearly at my own jeopardy and I am prepared to answer to all the consequences of this decision.

He and Russo faced charges under the Espionage Act of 1917 and other charges including theft and conspiracy, carrying a total maximum sentence of 115 years. Their trial commenced in Los Angeles on January 3, 1973, presided over by U.S. District Judge William Matthew Byrne, Jr.

On April 26, the break-in of Fielding's office was revealed to the court in a memo to Judge Byrne, who then ordered it to be shared with the defense.

On May 9, further evidence of illegal wiretapping against Ellsberg was revealed in court. The FBI had recorded numerous conversations between Morton Halperin and Ellsberg without a court order, and furthermore the prosecution had failed to share this evidence with the defense.

During the trial, Byrne also revealed that he personally met twice with John Ehrlichman, who offered him directorship of the FBI. Byrne said he refused to consider the offer while the Ellsberg case was pending, though he was criticized for even agreeing to meet with Ehrlichman during the case.

Due to the gross governmental misconduct and illegal evidence gathering, and the defense by Leonard Boudin and Harvard Law School professor Charles Nesson, Judge Byrne dismissed all charges against Ellsberg and Russo on May 11, 1973 after the government claimed it had "lost" records of wiretapping against Ellsberg. Byrne ruled: "The totality of the circumstances of this case which I have only briefly sketched offend a sense of justice. The bizarre events have incurably infected the prosecution of this case."

As a result of the revelation of the Fielding break-in during the trial, Ehrlichman, H. R. Haldeman, Richard Kleindienst and John Dean were forced out of office on April 30, and all would later be convicted of crimes related to the Watergate scandal. Egil Krogh later pled guilty to conspiracy, and White House counsel Charles Colson pled no contest for obstruction of justice in the burglary. "The court concluded that Nixon, Mitchell, and Haldeman had violated the Halperins' Fourth Amendment rights, but not the terms of Title III. The Halperins were awarded $1 in nominal damages in August 1977."

Ellsberg later claimed that after his trial ended, Watergate prosecutor William H. Merrill informed him of an aborted plot by Liddy and the "plumbers" to have 12 Cuban-Americans who had previously worked for the CIA to "totally incapacitate" Ellsberg as he appeared at a public rally, though it is unclear whether that meant to assassinate Ellsberg or merely to hospitalize him. In his autobiography, G. Gordon Liddy describes an "Ellsberg neutralization proposal" originating from Howard Hunt, which involved drugging Ellsberg with LSD, by dissolving it in his soup, at a fund-raising dinner in Washington in order to "have Ellsberg incoherent by the time he was to speak" and thus "make him appear a near burnt-out drug case" and "discredit him". The plot involved waiters from the Miami Cuban community. According to Liddy, when the plan was finally approved, "there was no longer enough lead time to get the Cuban waiters up from their Miami hotels and into place in the Washington Hotel where the dinner was to take place" and the plan was "put into abeyance pending another opportunity".

Reflecting on his time in government, Ellsberg has said the following, based on his extensive access to classified material:

The public is lied to every day by the President, by his spokespeople, by his officers. If you can’t handle the thought that the President lies to the public for all kinds of reasons, you couldn’t stay in the government at that level, or you’re made aware of it, a week. The fact is Presidents rarely say the whole truth...essentially, never say the whole truth...of what they expect and what they’re doing and what they believe and why they’re doing it and rarely refrain from lying, actually, about these matters.

Since the end of the Vietnam War, Ellsberg has continued his political activism, giving lecture tours and speaking out about current events. During the runup to the 2003 invasion of Iraq he warned of a possible "Tonkin Gulf scenario" that could be used to justify going to war, and called on government "insiders" to go public with information to counter the Bush administration's pro-war propaganda campaign, praising Scott Ritter for his efforts in that regard. He later provoked criticism from the Bush administration for supporting British GCHQ translator Katharine Gun and calling on others to leak any papers that reveal government deception about the invasion. Ellsberg also testified at the 2004 conscientious objector hearing of Camilo Mejia at Fort Sill, Oklahoma.

Ellsberg was arrested, in November 2005, for violating a county ordinance for trespassing while protesting against George W. Bush's conduct of the Iraq War.

In September 2006, Ellsberg wrote in Harper's Magazine that he hoped someone would leak information about a potential US invasion of Iran before the invasion happened, to stop the war. Subsequently, information on the acceleration of US-sponsored anti-government activity in Iran was leaked to journalist Seymour Hersh.

In November 2007, Daniel Ellsberg was interviewed by Brad Friedman on his Bradblog in regard to former FBI translator turned whistleblower Sibel Edmonds. "I'd say what she has is far more explosive than the Pentagon Papers", Ellsberg told Friedman.

In a speech on March 30, 2008 in San Francisco's Unitarian Universalist church, Ellsberg observed that House Speaker Nancy Pelosi doesn't really have the authority to declare impeachment "off the table". The oath of office taken by members of congress requires them to "defend the Constitution of the United States against all enemies, foreign and domestic". He also argued that under the US Constitution, treaties, including the United Nations Charter, become the supreme law of the land that neither the states, the president, nor the congress have the power to break. For example, if the Congress votes to authorize an unprovoked attack on a sovereign nation, that authorization wouldn't make the attack legal. A president citing the authorization as just cause could be prosecuted in the International Criminal Court for war crimes, and it is the duty of congress to impeach the offending president regardless of any agreements that may have been made.

On June 17, 2010, Ellsberg was interviewed by Amy Goodman and Juan Gonzalez on the Democracy Now! program regarding the parallels between his actions in releasing the Pentagon Papers and those of Pfc. Bradley Manning, who was arrested by the U.S. Military in Kuwait after allegedly providing to the WikiLeaks web site a classified video showing U.S. military helicopter gunships strafing and killing Iraqis alleged to be civilians, including two Reuters journalists. Manning reportedly claims to have provided WikiLeaks with secret videos of additional massacres of alleged civilians in Afghanistan, as well as 260,000 classified State Department cables. Ellsberg has said that he fears for Manning and for Julian Assange, as he feared for himself after the initial publication of the Pentagon Papers. WikiLeaks says it has not received the cables, but said it plans to post the video of an attack that may have killed 140 Afghani civilians in the village of Garani. Ellsberg expressed hope that either Assange or President Obama would post the video, and expressed his strong support for Assange and Manning, who he called "two new heroes of mine".

Ellsberg is the recipient of the Inaugural Ron Ridenhour Courage Prize, a prize established by The Nation Institute and The Fertel Foundation. In 1978 he accepted the Gandhi Peace Award from Promoting Enduring Peace. On September 28, 2006 he was awarded the Right Livelihood Award.

Daniel Ellsberg has been married twice. First to Carol Cummings (the daughter of a Marine Corps Brigadier General), a marriage that lasted 13 years and ended in a divorce (at her request, as he has stated in his memoirs titled "Secrets"). Two children (Robert and Mary) were born of this marriage. In 1970, he married Patricia Marx (whom he had dated earlier).A son (Michael) resulted from this marriage.

• Daniel Ellsberg. 2002. "Secrets: A Memoir of Vietnam and the Pentagon Papers." New York: Viking Press. ISBN 0-670-03030-9
• Daniel Ellsberg. 2001. "Risk, Ambiguity and Decision" Routledge. ISBN 0-8153-4022-2 (Ellsberg's 1962 PhD was released as a book)
• Daniel Ellsberg. 1972. "Papers on the War" Simon and Schuster. ISBN 0-671-21185-4 (Collection of essays and testimony)

Books with forward or introduction by Daniel Ellsberg:

• "Dissent: Voices of Conscience"-(publishers catalog P.1) by Ann Wright, Susan Dixon (Foreword by) Daniel Ellsberg, January 2008 - Publisher: Koa Books
• "Flirting with Disaster: Why Accidents are Rarely Accidental" by Marc S. Gerstein, Michael Ellsberg, (Foreword by) Daniel Ellsberg, June 2008 - Publisher: Sterling Publishing
• "Made Love, Got War: Close Encounters with America's Warfare State" By Norman Solomon, Foreword by Daniel Ellsberg, September 2007 - Publisher: Polipoint Press
• "Protest and Survive" by E. Thompson, Dan Smith, Introduction by Daniel Ellsberg, 1981 - Publisher: Monthly Review Press

• Official name of the Pentagon Papers: "History of United States Decision-Making Process on Vietnam Policy, 1945-1967".

• The New York Times version of Pentagon Papers: June 13, 14, 15 and July 1, 2, 3, 4 and 5, 1971. Late in this year this edited version was published in the book "The Pentagon Papers as published by N.Y. Times", Bantam Books, Toronto - New York - London, 1971.

• "United States-Vietnam Relations 1945—67, Department of Defense Study", 12 vols., Government Printing Office, Washington, 1971. This is the official and complete edition of the Pentagon Papers, published by the Government after the release by the press.

• UNGAR, Sanford, "The Papers and the Papers. An account of the legal and political battle over the Pentagon Papers", E.P. Dutton & Co, New York, 1972.