Former Auditor-General Martin Matthews claims he was forced out of his job in the fallout over how a serial conwoman was able to fleece $750,000 from a government department.

Matthews says he feels like his "scalp" was offered up by politicians who needed to get rid of him to please voters before the last election.

Matthews is addressing media this morning in a press conference with his lawyer and supporter Mary Scholtens QC.

Matthews was the head of the Ministry of Transport when fraudster Joanne Harrison stole $750,000. Harrison was jailed for the fraud and has now been deported from New Zealand. She also stole from a previous employer, Tower Insurance.

Once Matthews found out about the ministry fraud, he launched the investigation which eventually led to her conviction.

After his tenure at the ministry ended, Matthews was appointed Auditor-General - but he says he was forced by MPs to resign six months later.

Matthews today revealed details of his departure from the role in August 2017.

The last two years had been a "horrendous" time for his family – "it's changed our lives".

He had been turned away from a number of jobs where he felt he was well qualified – but he was asked to not apply as he was "too toxic".

He was highly critical of Harrison, calling her a "sociopath" who stole from her colleagues.

Matthews today unveiled a petition calling on Parliament to re-open his employment case, saying he was forced to resign.

Scholtens referred to Matthews as a "watchdog of the people" when he was the Auditor-General.

She said the Officers of Parliament Committee threatened Matthews because he was "disabled from performing his duty".

"He was not disabled," Scholtens said.

She claimed the group of MPs never made it fully clear why they asked Matthews to stand down.

"Effectively, a gun was held to his head by the committee," she said, adding that Matthews had six hours to decide if he was going to step down - or to face being removed.

"The actions against Matthews should be a concern for all New Zealanders," Scholtens said.

The committee's behaviour could not be allowed to stand – that's why she and Matthews had launched the petition.

It seeks an independent review into the committee's process and wants a payout for damages.

Scholtens said she had also written to Prime Minister Jacinda Ardern about this matter.

Matthews' reputation had been slaughtered, she said.

He told reporters it felt like he had paid a higher price than Harrison for her fraud - and that was not fair.

An emotional Matthews said he never once hesitated to do the right thing when it came to the Harrison saga.

The way he had been treated sent the wrong signal to New Zealanders - and to would-be whistleblowers who sought to help bring people who had done wrong to justice.

Matthews said he wanted to make sure that what happened to him could never happen to anyone else.

"They need to know they will be treated fairly."

He said the committee "held a gun to my head" and now he could not secure a job.

"I am now what is known as 'too toxic to touch'."

Matthews is calling on the Government to "put these wrongs, right" and wants Parliament to take immediate action to address his petition.

Asked for his message to the committee that "slaughtered" his reputation, Matthews said it was "totally inappropriate" for politics to get in the way of the work that the Auditor-General has to do.

He said it had been a "life-long" ambition to become Auditor-General.

He described himself as someone who will always "stand up for what is right".

Joanne Harrison stole $750,000 from the Ministry of Transport.

Matthews earlier told Stuff that MPs on the committee forced his resignation and the process had left him financial ruined and unemployable.

Documents regarding his hearing with the Officers of Parliament Committee – a group of MPs from across the House chaired by the then-Speaker David Carter – were thought to be suppressed.

But Stuff found the documents which showed Matthews was given an ultimatum: resign or be removed.

The documents show Carter said the committee had lost confidence in Matthews: "on the grounds of disability affecting the performance of duty".

That disability was on the grounds of a draft report into Matthews' handling of the Harrison saga when he was her boss at the Ministry of Transport.

Matthews is now petitioning Parliament to reopen his case.