[5] In 1983, he published the book Deadly Force, about a case of wrongful death and police brutality in which O'Donnell's father was the plaintiff's lawyer.

His aggressive debate style on that program and others led to several on-air confrontations, including an interview with conservative Marc Thiessen on Morning Joe that became so heated that Scarborough took O'Donnell off the air.

[17] On September 20, 2017, an eight-minute video clip was leaked; it showed O'Donnell angrily cursing and swearing about background noise between segments of a live broadcast that had aired on August 29, 2017.

In addition to being a producer on The West Wing, O'Donnell also played President Josiah Bartlet's father in a flashback sequence of the episode "Two Cathedrals".

"[24][25] In the April 3, 2012, broadcast of The Last Word, O'Donnell made comments regarding the Church of Jesus Christ of Latter-day Saints (LDS Church), saying it was an "invented religion," which was "created by a guy in upstate New York in 1830 when he got caught having sex with the maid and explained to his wife that God told him to do it.

In O'Donnell’s introduction to the taped interview, he said, "Michael Steele is dancing as fast as he can, trying to charm independent voters and Tea Partiers while never losing sight of his real master and paycheck provider, the Republican National Committee."

After these remarks drew criticism from Steele and talk-radio host Larry Elder, who both characterized them as racially insensitive, O'Donnell apologized for them.

[31] O'Donnell said he had not been part of any agreement, but an MSNBC spokeswoman stated, "We told Representative Paul's office that the focus would be on the tea party movement, not on specific candidates.

"[32] During an October 2011 interview, O'Donnell accused Republican primary candidate Herman Cain of not participating in protests during the 1960s civil rights movement and of avoiding the draft during the Vietnam War.

The Atlantic's Conor Friedersdorf called O’Donnell’s questions during the interview "offensive," adding, "In this interview, O'Donnell goes to absurd lengths to use patriotism and jingoism as cudgels to attack his conservative guest, almost as if he is doing a Stephen Colbert-style parody of the tactics he imagines a right-wing blowhard might employ.

[34] On August 27, 2019, O'Donnell reported that Deutsche Bank documents showed Russian oligarchs had cosigned loan applications for Trump.

O'Donnell based this report on a single source that he did not identify, although he used the qualifier "if true," and acknowledged that it had not been verified by NBC News.

"[37] On the August 1, 2011, episode of The Last Word, O'Donnell further explained: "I have been calling myself a socialist ever since I first read the definition of socialism in the first economics class I took in college".