[3][6][7] Brennan's 25 years with the CIA included work as a Near East and South Asia analyst, as station chief in Saudi Arabia, and as director of the National Counterterrorism Center.

[13] On August 15, 2018, President Donald Trump announced that he had revoked Brennan's security clearance, although the White House reportedly did not follow through with the revocation process.

[21] After Fordham, Brennan attended the University of Texas at Austin, receiving a Master of Arts in government with a concentration in Middle East studies in 1980.

[3] He was director of the newly created Terrorist Threat Integration Center from 2003 to 2004, an office that sifted through and compiled information for President Bush's daily top secret intelligence briefings and employed the services of analysts from a dozen U.S. agencies and entities.

[24] Brennan then left government service for a few years, becoming Chairman of the Intelligence and National Security Alliance (INSA) and the CEO of The Analysis Corporation (TAC).

However, Brennan withdrew his name from consideration because of opposition to his CIA service under President George W. Bush and past public statements he had made in support of enhanced interrogation and the transfer of terrorism suspects to countries where they might be tortured (extraordinary rendition).

He said that using the second term, which means one who is struggling for a holy goal, gives "these murderers the religious legitimacy they desperately seek" and suggests the US is at war with the religion of Islam.

[29] Brennan told The New York Times in January 2010, "I was somebody who did oppose waterboarding,"[30] a claim that he repeated in 2013, during the Senate's hearings about whether to confirm him as Obama's CIA director.

[1][33] Within two weeks after the incident, however, he produced a report highly critical of the performance of U.S. intelligence agencies, concluding that their focus on terrorist attempts aimed at U.S. soil was inadequate.

[23] In February 2010, he claimed on Meet the Press that he was tired of Republican lawmakers using national security issues as political footballs, and making allegations where they did not know the facts.

[35] In the aftermath of the operation, Brennan said that the U.S. troops in the raid had been "met with a great deal of resistance", and bin Laden had used a woman as a human shield.

[36][37] In April 2012, Brennan was the first Obama administration official to publicly acknowledge CIA drone strikes in Pakistan, Yemen, Somalia, Libya, Afghanistan, and elsewhere.

In 2011–2012, he also helped reorganize the process, under the aegis of the Disposition Matrix database, by which people outside of war zones were put on the list of drone targets.

[44] In June 2011, Brennan claimed that US counter-terrorism operations had not resulted in "a single collateral death" in the past year because of the "precision of the capabilities that we've been able to develop".

[46][47] The Bureau of Investigative Journalism disagreed with Brennan, citing their own research[48] that initially led them to believe that 45 to 56 civilians, including six children, had been killed by ten US drone strikes during the year-long period in question.

"[49] According to the Bureau of Investigative Journalism, Brennan's comments about collateral death are perhaps explained by a counting method that treats all military-aged males in a strike zone as combatants unless there is explicit information to prove them innocent.

[10][11] Morris Davis, a former Chief Prosecutor for the Guantanamo Military Commissions compared Brennan to Canadian Omar Khadr, who was convicted of "committing murder in violation of the law of war".

[55] Two months after assuming his post at the CIA, Brennan replaced Gina Haspel, head of the National Clandestine Service with another unidentified, career intelligence officer and former Marine.

[71][72] British security hacker Kane Gamble, sentenced to two years in youth detention, posed as CIA chief to access highly sensitive information and hacked into Brennan's private email and iCloud accounts, made hoax calls to his family home and even took control of his wife's iPad.

During a subsequent security conference at George Washington University, Brennan proclaimed his "outrage" at the hack but also demonstrated the need to "evolve to deal with these new threats and challenges".

[76][77] In January 2017, a North Carolina college student pleaded guilty in a Virginia federal court to charges relating to hacking Brennan's e-mail.

[78] The two North Carolina men eventually pleaded guilty to a conspiracy with a group that called itself "Crackas With Attitude" to commit unauthorized computer intrusions, identity theft, and telephone harassment.

[79] Brennan helped establish the FBI’s counterintelligence investigation of Donald Trump’s campaign, which included the use of foreign intelligence, during the period leading up to the 2016 presidential election.

[81] Following the firing of FBI Deputy Director Andrew McCabe later that month, Brennan tweeted to Trump: When the full extent of your venality, moral turpitude, and political corruption becomes known, you will take your rightful place as a disgraced demagogue in the dustbin of history.

[82]Axios quoted Brennan tweeting a response to Trump's harsh comments about James Comey: "Your kakistocracy is collapsing after its lamentable journey... we have the opportunity to emerge from this nightmare stronger & more committed to ensuring a better life for all Americans, including those you have so tragically deceived.

[85] Brennan was also the target of a mailed pipe bomb incorrectly addressed to "John Brenan", as were multiple other Democratic lawmakers, officials, and critics of Trump.

[14] She read a statement from Trump, dated July 26, that said Brennan's "lying and recent conduct, characterized by increasingly frenzied commentary, is wholly inconsistent with access to the nation's most closely held secrets and facilitates the very aim of our adversaries, which is to sow division and chaos".

[93] The statement said further, that Brennan had "recently leveraged his status as a former high-ranking official with access to highly sensitive information to make a series of unfounded and outrageous allegations – wild outbursts on the internet and television – about this Administration".

[99] On May 25, 2019, The New York Times reported that the administration had never followed through on the bureaucratic process to revoke Brennan's clearance as the attempt was "hampered by aides who slow-rolled the president and by Justice Department officials who fought Mr. Trump, warning he was jeopardizing national security".

[103] In October 2020, Brennan was one of a group of 51 former senior intelligence officials who released an open letter stating that the Hunter Biden Laptop Controversy "has all the classic earmarks of a Russian information operation".