Dr Tony Holohan, who led the response to the Covid-19 pandemic, is to step down from his position as Chief Medical Officer at the Department of Health.
He will take on a new role as Professor of Public Health Strategy and Leadership at Trinity College Dublin.
Dr Holohan was appointed as Deputy Chief Medical Officer in 2001, before taking over as Chief Medical Officer in December 2008.
He qualified as a doctor from University Hospital Dublin in 1991.
Most recently, he served as the chairperson of the National Public Health Emergency Team (NPHET), which provided advice to the Government in relation to the Covid-19 pandemic.
In a statement, Dr Holohan said "it has been a great privilege for me to serve as Chief Medical Officer and to have had an opportunity to be directly involved in issues of great importance and relevance to the health of the people of Ireland".
The outgoing CMO also paid tribute to those who he has worked alongside in his role.
He said "in particular, these past two years have presented extreme challenges to public health globally and I have been honoured to work alongside exceptional colleagues in the Department of Health, the HSE, the wider health service and across Government".
"During this time, I have witnessed the dedication of colleagues to protecting the health and wellbeing of people across Ireland," he added.
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The Taoiseach offered his sincere thanks to Dr Holohan for what he described as "more than two decades of outstanding and dedicated service to the people of Ireland in the field of public health".
Micheál Martin said his "work chairing the NPHET, his professionalism, and calm and personable nature gave us all the assurance we needed during the pandemic".
"His steadfast assured advice, and willingness to communicate over the course of the Covid-19 pandemic undoubtedly helped save lives, and kept Ireland safe during an exceptionally challenging two years," he added.
Tánaiste Leo Varadkar also paid tribute saying that hundreds, if not thousands, of lives were saved due to Dr Holohan's advice to the Government over the course of the Covid-19 pandemic.
Mr Varadkar said he had had the privilege of working alongside Dr Holohan as Minister for Health, Taoiseach and Tánaiste - in which they had dealt with some of the most sensitive issues, including CervicalCheck, drugs and alcohol policy, failings in maternity services and Covid-19.
Mr Varadkar said the CMO was always committed, available, clear and robust in his thinking and advice.
Minister for Health Stephen Donnelly said Dr Holohan has "made a significant and lasting impact on health in Ireland".
The minister said "throughout his time as CMO, Tony has used his public health leadership ability, alongside his many other skills and insights, to inform and influence decisions at the highest level in order to protect public health".
On his new appointment, Provost of Trinity College Dublin Professor Linda Doyle, said "we're excited that he will be working with other academic colleagues in Trinity to learn the lessons of Covid and prepare for these future challenges".
Thank you @CMOIreland Tony Holohan for your outstanding service to the Irish people, during the pandemic, and over 21 years in the CMO office.— Micheál Martin (@MichealMartinTD) March 25, 2022
Your dedication, and steadfast advice was crucial to Ireland's response, and saved lives.
Every success in your new role at @tcddublin
Minister for Further and Higher Education Simon Harris, who was Minister for Health during the early weeks of the pandemic, thanked Dr Holohan for his "service to our country".
He added: "I saw first hand your steady leadership, your work ethic, your determination and the personal sacrifices you made."
Sinn Féin's Health spokesperson David Cullinane also paid tribute to the departing CMO.
"He steered the state through a very difficult time over the last number of years. His professionalism and commitment to public health and public service is a credit to him and his family," he said.
Labour Party Health spokesperson Duncan Smith said Dr Holohan had made "an immense contribution to the Covid effort, which at the heart of it, was the desire to save lives and keep people safe".
Since his appointment as Chief Medical Officer, Dr Holohan has been around for many controversies.
When the scandal over the deaths of babies at the Midland Regional Hospital in Portlaoise in Co Laois, came to light, he was widely praised for his review into the affair in March 2014.
But the Limerick man also faced criticism over his handling of the CervicalCheck controversy in 2018, when he advised against any external review of the screening programme.
However, Dr Holohan gained most prominence from his involvement in Ireland's response to the Covid-19 pandemic.
As well as chairing meetings of the NPHET, he was also one of the firm fixtures at the daily and weekly press briefings over the last two years.
Following the recent lifting of Covid restrictions, NPHET was stood down, to be replaced by a monitoring group, which was due to be overseen by Dr Holohan.
Additional reporting: Fergal Bowers