Eoghan Murphy has resigned his seat as a TD for Dublin Bay South and is to pursue a career in international co-operation, human rights and democracy.
The move was announced in a statement issued by Fine Gael this morning.
In a letter sent to Fine Gael members in the Dublin Bay South constituency, Mr Murphy said leaving frontline politics is not something that he is doing without having considered the matter fully.
Mr Murphy said he had come to this "personal decision" and acknowledged that it may come as a "surprise".
He was a Fine Gael councillor, and served in the Dáil from 2011 as a TD, minister of state, and more recently he was Minister for Housing from June 2017 until June 2020.
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He wrote to the Ceann Comhairle of the Dáil to confirm his resignation.
Speaking on RTÉ's Today with Claire Byrne, Mr Murphy said he felt daunted but "excited" after announcing his decision to step down, and had "mixed emotions" this morning.
"I've been a politician for 12 years and it kind of defines you. It is how you kind of define yourself. I have been a member of Fine Gael for 12 years, and to be stepping away from that, it is tough. It's a bit daunting, but I'm also excited about the future as well.
"It's back to civilian life," he said.
He confirmed that he is no longer a TD, but is still a member of Fine Gael. "I remain fully committed to that," he added.
Mr Murphy explained that he had been "keeping Leo Varadkar in the loop" throughout his early thoughts about leaving the Dáil, and that he began to give it serious thought over Christmas.
"To be fair to him and everyone there were certain people I was trying to keep in the loop, as I was coming to this decision."
Prior to entering Leinster House, Mr Murphy was elected a Dublin City Councillor in 2009 for the Pembroke-Rathmines constituency.
"It has been a huge privilege to serve the Dublin Bay South constituency, first as a councillor and then as a TD," he said.
The resignation means that a by-election will have to be held in the Dublin Bay South constituency within six months.
Before running for the local elections in 2009, Mr Murphy spent four years working for the UN and the EU on issues such as nuclear disarmament.
His time at Cabinet proved challenging as the Government struggled to deliver housing and the numbers of people without a home continued to rise for most of the period he served as Minister for Housing.
The 39-year-old was a close political ally of the Tánaiste and played a significant part in Mr Varadkar's successful campaign to become Fine Gael Leader in 2017.
This morning, Mr Varadkar said he was aware that Mr Murphy was considering his career options recently, but he had hoped that he would stay in the Dáil.
"Eoghan took over the housing brief at a most difficult time. History will record that under his leadership, the provision of new social housing increased manifold and the Rebuilding Ireland Home Loan provided a mortgage to thousands of first-time buyers who otherwise would have got none," Mr Varadkar said.
However, Mr Murphy did not retain his place at Cabinet when the coalition was formed last June and he did not seek a junior ministerial role.
His departure opens up a fascinating electoral contest in his constituency. Well-known figures such as former Fine Gael TD Kate O’Connell and Green Party Chairperson Hazel Chu would be viewed as possible candidates.
Meanwhile, the National Organiser of the Labour Party said that party Senator Ivana Bacik is likely to contest the by-election.
Kevin Humphreys, a former TD in the constituency, said he predicts that it will be a very good by-election for the Labour Party, and there are three strong councillors in the mix supporting Ms Bacik's bid.
Sinn Féin too has confirmed it will run a candidate in the constituency, with a decision due in a few weeks on the individual.
Fianna Fáil is also expected to contest with one of its local councillors, Claire O'Connor or Deirdre Conroy.