Former Garda Commissioner Nóirín O'Sullivan has been appointed as the United Nations' Assistant Secretary-General for Safety and Security.

Ms O'Sullivan stepped down from her role with An Garda Síochána in September 2017.

In her statement last year, she said the "unending cycle" of scrutiny surrounding her role and the force as a whole.

Giving evidence at the Disclosures Tribunal earlier this year, she said she stepped down for the well-being of her family and due to the impact on An Garda Síochána of the controversy surrounding allegations against her.

The tribunal examined claims that Ms O'Sullivan was involved in a smear campaign against garda whistleblower Sergeant Maurice McCabe.

A report this month by tribunal chairman Justice Peter Charleton accepted Ms O'Sullivan's evidence that she never suggested that Sgt McCabe's integrity be challenged at the O'Higgins Commission.

Ms O'Sullivan joined the gardaí in June 1981 and had more than 36 years of service at the time of her retirement.

The 58-year-old will be responsible for the day-to-day overall management of the Department for Safety and Security.

Read more: Commissioner says retiring McCabe has done a great service