Ms Holgate controversially departed Australia Post after Mr Morrison angrily condemned her over a luxury watches scandal in parliament.
"I lost my job, a job that I loved, because I was humiliated by our prime minister for committing no offence and then bullied by my chairman," she told the committee.
She alleged Mr Di Bartolomeo unlawfully stood her down under the direction of the prime minister, making her leadership untenable and threatening her health.
"I have done no wrong. Their bullying of me was far from over. I was subjected to a biased investigation and intimidated with constant threats of further allegations and criticism," Ms Holgate said.
In a subsequent interview with the ABC aired on Tuesday evening, Ms Holgate said the prime minister's remarks in parliament was "one of the worst acts of bullying I have ever witnessed".
Earlier, she told the Senate hearing the tone of her email to government ministers asking for a meeting about her job showed the damage to her mental health.
"If you read that note and I apologise in advance, that it is rambling and it is rambling because I was seriously ill. I was on temazepam. I was suicidal," she said.
Ms Holgate accused Mr Di Bartolomeo of throwing her under a bus so he could "curry favour" with political masters.
She said all but one member of the Australia Post board had close ties to the coalition and rejected its independence.
She told senators to ask Telstra for phone records, which she believes will reveal she never agreed to stand down as suggested by the chairman.
With local post office operators and some politicians agitating for her to be reinstated, Ms Holgate declared Mr Di Bartolomeo would need to leave for her to return.
The Morrison government announced Woolworths supply chain boss Paul Graham as Ms Holgate's replacement one day before the much-anticipated hearing.
The ex-Post chief said she was humiliated in a way no male public servant was subjected to.
"Do I believe it's partially a gender issue? You're absolutely right I do," Ms Holgate said.
"But do I believe the real problem here is bullying and harassment and abuse of power? You're absolutely right I do."
In a blistering opening statement, a defiant Ms Holgate said she wanted to speak out to stop workplace bullying and harassment.
"This is a day the chairman of Australia Post and the other men involved in what happened to me will be held to account."
Holgate 'treated abysmally'
Mr Di Bartolomeo gave evidence to the Senate committee on Tuesday afternoon, where he conceded Ms Holgate was treated poorly by "parliament and media" but said the Australia Post board did not owe her an apology.
In his opening statement, he said Ms Holgate was a "very good chief executive for Australia Post" and viewed her purchase of the luxury watches as an "error of judgement made in good faith".
"I also recognise the circumstances around the departure of the former CEO were difficult for Christine and everyone involved," he said.
"All through the process, her welfare remained a priority for Australia Post and we made sure the organisation continued to support her through what has been a trying time."
Mr Di Bartolomeo said he thought Ms Holgate had been treated "abysmally", but he believes the board and management "did the right thing by her".
“I don’t believe Australia Post owes her an apology, no. But I do believe she was badly treated," he said.
The chairman last week denied Ms Holgate's claims that he unlawfully stood her down, and said she was provided "confidential and regular support".
He maintained his position on Tuesday that Ms Holgate "stood aside", saying neither he nor the board sought Ms Holgate's resignation.
He said Ms Holgate's poor treatment followed Mr Morrison telling parliament on 22 October she "can go" if she did not stand aside for an investigation.
“The environment that was created at the time - from that afternoon on through parliament and the media thereafter, and everyone else who bought in - created a set of circumstances that made her job, her life very difficult,” Mr Di Bartolomeo said.
'We did not hound her out of a job'
Mr Di Bartolomeo said he wanted Ms Holgate to stand aside for four weeks while an independent investigation was held so the company could appoint a temporary CEO to "execute the largest parcel delivery exercise" during the COVID-19 pandemic.
He said Communications Minister Paul Fletcher called him on two occasions before Question Time on 22 October, advising he wanted an independent review of the circumstances and for Ms Holgate to stand aside during that time.
"He [Fletcher] wanted us to support the investigation. And he wanted us to look at standing Christine down. I queried whether that was what he really wanted. He said, ‘Look, I am going to come back to you’. We had the later discussion where that was all reaffirmed," he said.
Mr Di Bartolomeo said he has "never in his life" spoken to the prime minister, nor spoke to him on that day. He said he did not take Mr Fletcher's calls as a "formal direction".
He insisted Ms Holgate agreed to stand aside - which she claims is a lie - before resigning less than two weeks later.
"If she did not do that, then we would have had to consider whether we would take other action," he said.
When asked by Greens Senator Sarah Hanson-Young whether it was right to "hound" Ms Holgate out of her job, Mr Di Bartolomeo replied: "We did not hound her out of a job".
"But you didn't stand up for her either," Senator Hanson-Young said.
Mr Di Bartolomeo rejected Ms Holgate's calls for him to stand down, saying board stability is essential.
"Australia Post has been taken through a very difficult patch and my view is until I believe differently I will not be resigning," he said.
In the ABC interview aired on Tuesday evening, Ms Holgate called the chairman's treatment of her "absolutely appalling".
“I don’t know another chairman in this country who would have treated their CEO leadership team how I’ve been treated. I think it’s absolutely appalling," she said.
Ms Holgate expressed frustration during the Senate hearing there were coalition MPs "accused of the most terrible atrocities to women" allowed to remain in their jobs while she was forced to stand down.
Former attorney-general Christian Porter has emphatically denied historical rape allegations against him and launched legal action against the original reporting of the claims.
Additional reporting by AAP.
Readers seeking support can contact Lifeline crisis support on 13 11 14, Suicide Call Back Service on 1300 659 467 and Kids Helpline on 1800 55 1800 (for young people aged 5 to 25).More information is available at Beyond Blue.org.au and lifeline.org.au. Embrace Multicultural Mental Health supports people from culturally and linguistically diverse backgrounds.