Klein grew up in Philadelphia and graduated from Torah Academy Boys High School in Philadelphia. In his book Schmoozing with Terrorists, Klein describes his upbringing: "I was a Talmud-studying Modern Orthodox Jew. I attended Jewish religious schooling my entire life from religious elementary school until college. I came from a tight-knit orthodox Jewish community."
At Yeshiva University in New York City, Klein edited the undergraduate bimonthly student newspaper, The Commentator and changed his major from biology to English upon becoming editor. Articles published in The Commentator regarding events such as use of an eight million dollar gift to the school and the removal of a secretary, written while Klein was a co-editor in chief, allegedly caused the school administration to remove some issues from circulation. This prompted the paper's editorial board to threaten to sue the University, generating national media attention. Yeshiva University later signed a contract with Klein in which it agreed to discontinue the practice and reimburse The Commentator for the confiscated issues.
Klein has a weekly talk show entitled "Aaron Klein Investigative Radio" on WNYM-AM 970 in Metro New York and WNTP-AM 990 in Philadelphia. His show includes his calling and interviewing terrorists on the air. "Aaron Klein Investigative Radio" was one of two weekend programs in the U.S. that made the list. The show is reported to have over one million weekly listeners.
In January 2013, the show claimed it was the most listened to AM talk show radio on the weekend.
A Jerusalem Post magazine profile, describing Klein as a "one man power house," quoted the radio host on why he thinks covering the U.S. while living in Tel Aviv is advantageous. "I have a major advantage being in Israel,” Klein told the newspaper. “For example when a child is raised in a dysfunctional household, sometimes he doesn’t realize the reality of the situation until he leaves and takes a look at things from the outside. Being here in Israel I have the advantage of exploring U.S. politics with a proper perspective, where I can see things far more clearly.”
On October 16, 2009, the National Journal reported Klein was also advocating against other Obama officials, including Cass Sunstein, the Administrator of the White House Office of Information and Regulatory Affairs. On Dec 1, 2009, Aaron Klein reported on the John Batchelor Show that Van Jones continues working for the White House, only as an independent consultant, and that the mainstream media is not reporting on the story.
In April 2008, Klein appeared on the John Batchelor radio show, where both interviewed Ahmed Yousef, chief political adviser to Hamas in the Gaza Strip. During that interview, Yousef stated that Hamas endorsed Barack Obama for president. Obama's chief political strategist, David Axelrod, said he was "flattered" by the Hamas comparison of Obama to President John F. Kennedy. Yousef's comments garnered media attention and were used as a campaign fundraising tool by Obama's opponent, the Republican presidential candidate John McCain. The interview was also noted by Pennsylvania media just before a presidential primary in that state between Obama and Sen. Hillary Clinton in which Clinton was victorious. The Pittsburgh Tribune-Review wrote an editorial entitled, "Hamas & Obama: Terrorist Flatter," questioning Axelrod's response to Hamas' endorsement. Ultimately, McCain and Obama themselves addressed Yousef's comments; McCain quoted Yousef's comments dozens of times during media interviews.
During a June 2007 interview, after an argument over whether or not Hamas was a terrorist organization, the British politician George Galloway evicted Klein and Rusty Humphries from his office and turned them over to Parliament police, claiming the two had breached security by falsely presenting themselves as reporters.
In June 2010, Imam Faisal Abdul Rauf, the Muslim leader behind a proposed Islamic cultural center near the site of the 9-11 attacks, was interviewed by Klein on WABC, where he reportedly refused to describe Hamas as a terrorist organization.
On August 15, 2010, Doctor Mahmoud al-Zahar, the chief of Hamas in Gaza, appeared on Klein's program, where he expressed support for Park51 community center. Zahar's comments made the cover of the New York Post and generated world media attention.
During the 2016 U.S. presidential election, Klein conducted a series of interviews with three of the sexual assault accusers of Bill Clinton; Juanita Broaddrick, Gennifer Flowers, Paula Jones and Kathleen Willey. The allegations become fodder for the presidential debates and the news cycle. Hours before the third presidential debate, former Arkansas television reporter Leslie Millwee gave her first public interview with Klein at Breitbart News, claiming Clinton sexually assaulted her in 1980.
In one of his first post-inaugural interviews Steve Bannon, Donald Trump's chief strategist, referred in the Wall Street Journal to Breitbart Jerusalem -- “Breitbart is the most pro-Israel site in the United States of America ... I have Breitbart Jerusalem, which I have Aaron Klein run with about 10 reporters there”. McClatchy News followed up, visiting Klein in Tel Aviv, profiling his working life and operation and how it fit into his year-and-a-half with Breitbart and into his career back to college.
Klein's book, Schmoozing with Terrorists: From Hollywood to the Holy Land, Jihadists Reveal their Global Plans – to a Jew!, was released in September 2007.
The book is based on interviews with purported terrorists. Topics include Klein's meetings with a recruited Palestinian suicide bomber; interviews with Muhammed Abdel-El, the head of a Popular Resistance Committee, and Hamas leader Sheikh Yasser Hamad, and confrontations with the Muslim desecrators of Jewish and Christian holy sites. There is also a section in which jihadist leaders are petitioned to describe what life in the U.S. would be like under the rule of Islam, a chapter on Christian persecution in the Middle East, and a chapter claiming the U.S. funds terrorism.
The Manchurian President: Barack Obama's Ties to Communists, Socialists and Other Anti-American Extremists was released in May 2010. In the book, (per the New York Times blurb), "President Obama's life and campaigns are sifted for Communist and socialist ties." The book was on the Times' bestseller list for hardcover nonfiction as well as those of Publishers Weekly and the Washington Post. Simon Maloy, writing for Media Matters for America, and John Oswald, of New York Daily News, both called the book "ridiculous crap." Some journalists, including from publications such as Time and Newsweek, sent emails to the author's publicist saying they did not want to receive a review copy of Klein's book.
Red Army:The Radical Network That Must Be Defeated to Save America was reviewed by Michael Tomasky for the New York Review of Books, writing "I can't in good conscience recommend that anyone read 'Red Army' except perhaps the president," noting that the book "will be read by hundreds of thousands."
Fool Me Twice: Obama's Shocking Plans for the Next Four Years Exposed was released on August 7, 2012, and appeared on the NY Times bestseller list the following week.
In August 2013, Klein published “Impeachable Offenses: The Case to Remove Barack Obama from Office.” MSNBC reported the book fueled the national conversation to impeach Obama, while BuzzFeed announced the book “ushers in the Obama impeachment movement” on the right.
On September 11, 2014, the second anniversary of the Benghazi attacks, Klein released a new book entitled, “The REAL Benghazi Story: What the White House and Hillary Don’t Want You to Know.”
Maggie Haberman reported in Politico that the book was part of a resurgence of conservative book publishing targeting Clinton in the run up to the United States presidential election in 2016. Alex Seitz-Wald, writing for MSNBC, said the book would prove "easy fodder for the conservative echo chamber."
In March 2009, Klein criticized Wikipedia for what he described as preferential treatment of Barack Obama coverage. Klein said that Wikipedia editors had scrubbed the article of material critical of the president and that an editor had been suspended for attempting to add "missing" details about Obama's relationship with Bill Ayers and allegations that Obama was not born in the United States. Klein said similar negative content was found in the article of George W. Bush.
The story was picked up by The Independent, The Daily Telegraph, Drudge Report and Fox News. A spokesperson for Wikipedia stated that the Obama article had not received any preferential treatment and another spokesperson noted the site's content is monitored and edited entirely by users. "Editors are really, really trying to do this as neutral as possible".
Klein removed the name of the editor from the article after reports arose on blogs and Wired News that he might himself be the suspended editor described in the story (the editor's only previous work on Wikipedia was editing Klein's page). In an email sent in response to the Wired News article, Klein wrote that the editor "works with me and does research for me."