Nóirín O'Sullivan was the first woman to become Garda Commissioner. She has been a member of the force for 36 years, serving at every rank.

In her role as head of An Garda Síochána, she had seen several garda controversies, including the falsification of garda breath tests, financial irregularities at the Garda College and questions about the treatment of whistleblowers.

'Dissent should not be seen as disloyalty'

From the outset, Ms O'Sullivan signalled there should be a change of attitude towards whistleblowers while she was in the top job.

In her first public comments as Interim Commissioner she said she felt very strongly that dissent should not be seen as disloyalty.

She was appointed to the role after the sudden departure of Martin Callinan. Just months before - she was seated beside him when he made remarks about the behaviour of whistleblowers.

At the Public Accounts Committee, the then-Commissioner addressed allegations being made by whistleblowers saying "frankly I think it's disgusting".

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First woman commissioner in male-dominated job

Ms O'Sullivan was appointed the first woman commissioner in a predominantly male force after an open, international competition.

Months later she ordered one of the biggest managerial shake ups of the organisation.

She later rejected charges of nepotism insisting the promotions system was fair and impartial. Questioned about it at the Oireachtas Justice Committee, she said: "There's lots of factual inaccuracies in the public domain, so lest that one of them remain that I promoted my bridesmaid that certainly isn't the case, because I didn't have a bridesmaid."

O'Sullivan faced many challenges in role

As Garda Commissioner she faced many challenges - the attack at the Regency Hotel raised questions about the level of garda intelligence. More resources were given. A new armed support unit and crime task force were set up. Major drugs and firearms seizures followed.

There were other challenges as well for the head of the force. A garda strike was averted at the eleventh hour.

Rank and file gardaí had planned four days of industrial action in November 2016 in a row over pay.

Ms O'Sullivan had issued a directive to gardaí that they must attend for work. However, gardaí were ready to go ahead with their protest up until the Garda Representative Association (GRA) and the Association of Garda Sergeants and Inspectors called off the strike action at the last minute.

The GRA said it was calling off the strike to consider a Labour Court recommendation which was later accepted by its members.

Questions raised over treatment of whistleblowers

But questions about the treatment of whistleblowers - including Sergeant Maurice McCabe continued. He first raised concerns about penalty points being quashed in 2008.

Inquiries, audits and reports followed: including the O'Higgins Report. Soon after its publication the Commissioner had to deny claims that her legal team had been instructed to question Sgt McCabe's integrity.

Then, former garda press officer Dave Taylor claimed in a protected disclosure there had been an orchestrated campaign directed by senior officers - to smear Sgt McCabe.

But the Commissioner denied any involvement. Speaking in a radio interview on RTÉ's Today with Sean O'Rourke, she said "I'm not aware, nor was I aware, of any campaign to discredit any individual".

But the treatment of whistleblowers was thrown back in the spotlight with revelations of a false allegation of sexual abuse made against Maurice McCabe in a file held by TUSLA. It led to the establishment of the Disclosures Tribunal. There were a number of calls for her to consider stepping aside for the duration of the Tribunal.

Government continues to defend commissioner

The Government continued to defended her and she insisted she was not guilt of anything.

Despite the majority of TDs wanting her to go, she indicated she would not be standing down.

"I have a journey of work that I have to do," she said. 

With controversy over her account of a meeting over finances at the Garda College in Templemore there were more calls for her to go.

With revelations this week of almost 500,000 extra falsified breath tests, the figures then neared 1.5 million. 

And after a second report on the fixed charge penalty system revealed 15,000 wrongful convictions, there were yet more calls for her to go.

This evening the Minister for Justice issued a statement saying he had been notifed by Ms O'Sullivan of her intention to retire today.