Newman explained to the show's host, Chuck Todd, that she recorded that conversation, as well as others she has played for reporters and book publishers featuring her conversations with Trump, because "this is a White House where everybody lies".
But the Situation Room recording raised questions about whether she had breached security protocols in a room that is supposed to be devoid of personal electronic devices.
"Who in their right mind thinks it's appropriate to secretly record the White House chief of staff in the Situation Room?" tweeted Ronna McDaniel, chair of the Republican National Committee.
The Situation Room is a Sensitive Compartmented Information Facility, or SCIF, and staff are not permitted to bring in mobile phones or other recording devices.
"I've never heard of a more serious breach of protocol," said Ned Price, who served as spokesman of the National Security Council in the Obama administration. "Not only is it not typical, something like this is unprecedented."
"If I didn't have these recordings, no one in America would believe me," Newman said on Sunday.
Trump has long been known to tape conversations over the phone and in person in his office at Trump Tower. He has threatened to produce tapes in the past as a way to instill fear in enemies, such as fired FBI Director James Comey.
In turn, Newman and another former Trump employee, Michael Cohen, who was once his personal lawyer, both taped key moments involving their time with Trump. White House officials and Trump have portrayed Newman and Cohen, who is under investigation in New York, as disgruntled and discredited figures.
"I think it's incredibly important in Trump world that you protect yourself, because everyone constructs their own reality," Newman told The New York Times on Sunday. "People around him try to reinforce that manufactured reality."
Newman claims that in one tape, Trump uses a racial slur in off-camera remarks during his time on The Apprentice. She describes the tape in her book but has said she does not have it herself.
When Todd asked Newman if she had ever heard the President say the slur, she said, "You know, I was in his presence when he said inappropriate things, but he has never said the N-word in my presence. Ever." She did not say which "inappropriate things" she had heard.
But she said that, after finishing her book, she had gone to Los Angeles to visit a person who had a copy of the tape in which Trump is said to use the slur. "I heard his voice, as clear as you and I are sitting here," she told Todd, adding: "It confirmed that he is truly a racist."
As Todd read quote after quote over several years in which Newman defended Trump in public, she said she had played a role in selling the administration's version of reality to the public, calling herself "totally complicit".
"In fact, I had a blind spot where it came to Donald Trump," she said. "I wanted to see the best in him. And obviously I, I felt miserably."
On ABC News This Week, White House counsellor Kellyanne Conway was pressed on Newman's claim that she was offered a hush-money contract with the Trump re-election campaign for $US15,000 ($20,000) a month. It is the same amount that a few others who have departed the White House under inauspicious circumstances are receiving.
Conway said "that is not what was offered" to Newman. She acknowledged that all West Wing officials had signed non-disclosure agreements, a measure that Trump relied on for decades as a real estate developer.
"Why wouldn't we?," she asked when the host, Jon Karl, pressed her on the issue.
Former White House lawyers and government ethics experts have said the agreements raised serious legal questions and reflected Trump's refusal to submit to the norms of public disclosure or respect free speech rights.
Conway said Newman was manufacturing events.
"I have worked alongside that man for over two straight years now without interruption; I have never a single time heard him use a racial slur about anyone," she said. "And it's — and I also never heard Omarosa complain that he had done that. And so the only thing that's changed is that she's now selling books."
New York Times, AP