Green Party councillor Pippa Hackett has been elected unopposed to the Seanad.
The election followed the departure of the party's Grace O'Sullivan from the Seanad after she won a seat in the European Parliament earlier this year.
The Green Party was the only party which selected a candidate for the vacancy.
The election of Ms Hackett was confirmed by the Clerk of the Seanad Martin Groves today.
In a statement Ms Hackett said: "I will be a voice for women, for our natural environment and heritage, and for the welfare of our animals."
Green Party Leader Eamon Ryan TD said Pippa Hackett brought experience as a "mother, farmer and councillor".