The current Lord Mayor of Dublin Paul McAuliffe has just been elected to the Dail after securing a seat in Dublin North West.
The Fianna Fail councillor pipped Solidarity-People Before Profit's Conor Reddy to the final seat in the three seat constituency.
But McAuliffe's elevation to Leinster House means that he must give up his seat on Dublin City Council.
It used to be the case that TDs and Senators could still hold their council seat but this was brought to an end with the signing into law of the Local Government Bill in 2003.
When a councillor resigns their seat, the political party who originally nominated the councillor who caused the vacancy nominates a new councillor and the council then passes a resolution to appoint the new member.
As Paul McAuliffe if also the Lord Mayor of Dublin, he will also relinquish that role.
A Dublin City Council spokeswoman told Dublin Live: "Following the election of Paul Mc Auliffe to the Dáil, the Deputy Lord Mayor, Tom Brabazon will take on the role of Lord Mayor until the next Council meeting where a new Lord Mayor will be elected."
Several more of Dublin's newly elected TDs will now have to resign their council seats.
These include Chris Andrews, Neasa Hourigan, Gary Gannon, Emer Higgins, Roderic O'Gorman and Paul Donnelly .
