Ivana Bacik is the new leader of the Labour Party.
The leadership contest came following the sudden resignation of Alan Kelly earlier this month.
No other candidate came forward to contest the position, and it had been widely expected that Ms Bacik would take over.
“I am honoured, excited, and I confess quite overwhelmed,” she said on Thursday, to applause.
She said that she grateful for the support of party members and paid tribute to her predecessor Alan Kelly, calling him her “friend and comrade”.
The pair embraced after her election was announced.
“I know the ambition you have for our future and for how our party can shape our future for the better,” she told the audience in Ringsend, a traditionally working-class area of Dublin.
“I sincerely hope that I can repay the trust you have placed in me.”
The Labour TD for Dublin Bay South was elected to the Dail last summer in a byelection after more than a decade as a senator.
Her fellow TDs Duncan Smith and Aodhán Ó Ríordáin, seen as possible contenders, quickly ruled themselves out of any contest.
The resignation of Mr Kelly, while unexpected even in some Labour Party circles, came after months of static poll ratings.
Ms Bacik will be charged with uniting the party and convincing voters to once again back Labour, which is still struggling with the legacy of its time in the Fine Gael-led coalition Government, which oversaw harsh austerity measures in the aftermath of the financial crash.
In her acceptance speech, Ms Bacik spoke of her feminist credentials and her history of activism dating back to her student days.
She also referenced John and Pat Hume, speaking about the impotence of a state that “works for the unity of the people of Ireland”.
“I didn’t become a political activist because I had all the answers – and I still don’t.”
Addressing an audience that included her mother, Ms Bacik said: “For me, politics is about building a better future.
“It’s not contrived shouting matches or tearing people apart to score a political point.”
She said that her politics was “constructive.”
“It’s about positive change.”
