Former housing minister and Fine Gael TD Eoghan Murphy has resigned his seat for Dublin Bay south.
The shock departure comes after 12 years as an elected representative, with Mr Murphy set to take up a career in international affairs.
Mr Murphy was first elected as a local councillor in 2009 before moving to the Dail in 2011, where he served as minster of state for financial services under Taoiseach Enda Kenny, before being promoted to Cabinet under Leo Varadkar.
He lost his seat at Cabinet in 2020 following the formation of the coalition government.
In a letter to Fine Gael members on Tuesday morning, Mr Murphy said it was "a personal decision" to resign his seat.
He said: "Leaving frontline politics is not something that I am doing without having considered the matter fully.
"In my late 20s, I worked in the UN system before I returned to Ireland to get involved alongside many other people looking to play their part in the national recovery at the time.
"Now, after 12 years of service and having reflected upon things, I have made the decision to return to international affairs.
"I want to thank all who I have worked alongside in Fine Gael, in the Oireachtas, in various Government departments, in Dublin City Council and numerous other agencies and bodies who serve the Irish people so well."
A by-election will now be held in the Dublin Bay South area, where possible candidates could include former Fine Gael TD and one-time rival Kate O'Connell.
Dublin Lord Mayor and Green Party member Hazel Chu has previously represented the Pembroke area on Dublin City council, although she has recently fallen out with party leadership following an unsuccessful Seanad run.
Murphy's time as a Cabinet minister was marked by a tumultuous period in housing, with Ireland experiencing record levels of child and family homelessness.
Monthly homeless figures of more than 10,000 increased the pressure on the minister, although he survived a motion of no confidence from the opposition in 2019 by 56 votes to 53.
In his letter to Fine Gael members, he described his time as housing minister as "the most challenging I faced in my time in politics".
He added: "We overcame obstacles in some areas and were defeated in others.
Tanaiste Leo Varadkar, a close ally of Murphy's, has paid tribute to the outgoing TD.
He said: "I am very sorry, personally and professionally, to see Eoghan departing from national politics.
"He is a friend and a colleague in the party, and someone with whom I have worked alongside for many years.
"I was aware for some time that Eoghan was considering his career options, although I had hoped that he would stay in the Dail, given his abilities, flair and talents."