She said many of the claims made about her work providing advice for the establishment of the AWU Reform Association were defamatory.
She blamed Opposition Leader Tony Abbott for fanning the flames.
"He has been engaged in relentless negativity since Australians voted in 2010," she said. Ms Gillard said she had ended her relationship with union official Bruce Wilson after hearing rumours about what was happening in the Victorian branch of the AWU.
"In those circumstances I came to a personal decision about ending my relationship," she told reporters.
"I did not have in front of me any evidence of criminality of wrongdoing."
The prime minister said there had been a focus on what she should have reported to authorities at the time.
"Well, you can't report things you do not know," she said.
"I did not know about transactions on the accounts of the AWU Workplace Relations Association."
Ms Gillard said her only role was to provide legal advice about the incorporation of the association.
"I did not set up a fund. I did not set up a bank account," the prime minister said.
"Any such claim about me is a defamatory claim."
Ms Gillard reiterated answers she gave during a "marathon" press conference in August.
"I acted on client instructions," she said.
"In terms of the use of the word slush fund, I said very specifically I did not think that that helped with the understanding of this matter.
"My understanding on the instructions provided by my clients was that this was an association which would support the re-election of union officials running on a particular platform of change, hence its name."
She said she had answered questions on this matter in 1995, 2001, 2006, 2007, as well as 2012.
Ms Gillard said the establishment of the AWU Reform Association did not strike her at the time as a "non-standard transaction" because it was common for union officials seeking re-election to incorporate such associations.
"Dealing with this matter during my legal career ... at the time (it) struck me as pretty routine, pretty low level, indeed so low level I didn't even charge for it," she said.
"It was being set up to support the re-election of a team of union officials in the AWU, hence the name, and they were intending to stand on a certain platform, hence the objects of association."
She said people planning to seek office at union elections often set up such incorporated associations as a way of keeping track of funds raised, in case they split up before the poll.
Ms Gillard rejected claims by former senior AWU official Ralph Blewitt, who says she has questions to answer and last week gave statements on three AWU-related matters to Victorian police.
"Let me remind you who Mr Blewitt is," she said.
"Mr Blewitt is a man who has publicly said he was involved in fraud.
"Mr Blewitt is a man who has sought immunity from prosecution.
"Mr Blewitt is a man who has fled Indonesia to avoid a police interview in relation to land fraud, although he denies wrongdoing in the case.
"Mr Blewitt says he owes money on another Asian land deal.
"Mr Blewitt admits to using the services of prostitutes in Asia.
"Mr Blewitt has published lewd and degrading comments and accompanying photographs on his Facebook page.
"Mr Blewitt, according to people who know him, has been described as a complete imbecile, an idiot, a stooge, a sexist pig, a liar and his sister has said he's a crook, and rotten to the core.
"His word against mine: make your mind up."
The prime minister was also quizzed about claims by former union employee Wayne Hem.
Mr Hem says he deposited $5000 cash into Ms Gillard's bank account in July 1995 at the request of AWU official Bruce Wilson, with whom she was then in a relationship.
Ms Gillard said the claim was "smear" because it related to her personal life.
The Labor leader added she didn't remember $5000 being put into her bank account.
"It is a long time ago so I have taken steps to try and check," Ms Gillard said.
"I specifically made inquires with the Commonwealth Bank ... they have advised me it is not possible to get records from 17 years ago."
Ms Gillard defended dealing directly with Mr Blewitt and Mr Wilson, rather than the union more broadly, because they were both AWU office holders.
In creating the AWU Workplace Reform Association, Mr Wilson and Mr Blewitt had acted as representatives of a team of officials who were going to run together for election in the trade union.
"Did I need to separately advise the AWU that this was occurring? Of course I didn't," she said.
"People I was dealing with were elected officials of the AWU."
The prime minister said she didn't think anyone in her office had been in touch with Mr Wilson, who on the weekend said Ms Gillard had done nothing wrong and "knew absolutely, categorically nothing that went after" the AWU entity had been created.
"In terms of contact between my office and Mr Wilson - (there was none) not to my knowledge," she said.
Ms Gillard added the Liberal party had been peddling the AWU matters around since 1995.
Questioned further about the $5000 allegedly deposited in her account, Ms Gillard said there was nothing unusual in her relationship with Mr Wilson that led her to think there was lots of unexplained money going around.
"We'd go out for dinner, sometimes he'd pay, sometimes I'd pay, sometimes we'd split the bill," she said.
"If I'm in a personal relationship, where the way in which it works in terms of expenditure is basically garden variety for personal relationships, then what is it that is supposed to have alerted my suspicion?
"There was nothing that happened which would lead me to conclude that there was somehow lots of money around, or lots of benefits around, that somehow I couldn't explain."
Ms Gillard wrapped up the 50-minute press conference with a rhetorical flourish.
"What I can confidently say is I did nothing wrong," she said.
"These things have been cycled and recycled and re-recycled and re-recycled over 20 years.
"I did nothing wrong."
The prime minister said when Mr Abbott and his deputy Julie Bishop were asked to articulate what it was she had allegedly done wrong "they are unable to do so".
- AAP
