Joan Burton says she now has to win the trust of the Irish people. The Social Protection Minister is the new leader of the Labour Party and is Tánaiste-designate.
She took 2,094 votes, with her only rival - Alex White - reaching 607.
Eamon Gilmore has already resigned from that position to facilitate her appointment by the Taoiseach Enda Kenny this evening.
In a statement to the Taoiseach earlier, Mr. Gilmore said he was stepping down to enable a successor to be appointed "at the earliest possible time".
Eamon Gilmore congratulates Joan Burton
He also thanked the Taoiseach "for his courtesy and co-operation", saying it was "a privilege and honour to work with him" during a very difficult time in the country's history.
The Junior Minister Alan Kelly has also won the deputy leadership of the party.
Arriving for the official declaration at the Mansion House in Dublin, Joan Burton says her job is making the country better for everybody.
The former party leader and Tanasite Eamon Gilmore has paid tribute to his successor.
Once the celebrations have died down in Labour Joan Burton will have a telephone conversation with the Taoiseach Enda Kenny this evening to formally begin the refreshing of the government.
Full talks will get underway on Sunday night or Monday morning.
