Mary Lou McDonald is seen by many as the face of a new generation of republicans.
She has no IRA baggage and hails from a middle-class part of Dublin, where she went to a private fee-paying school.
The mother-of-two, who now lives in Cabra, Dublin, has been clear favourite for some time to replace Gerry Adams, one of the longest serving party leaders in the world.
Sinn Fein’s president elect Mary Lou McDonald at the party’s special conference at the RDS in Dublin (Niall Carson/PA)
She was once described by her party colleague Caral Ni Chuilin as “one of the most formidable women in politics”.
Born in 1969, Mrs McDonald’s background is very different from other leading Sinn Fein politicians.
She was raised in the affluent Rathgar area of Dublin and was educated at Notre Dame, a private fee-paying school in the city. She is a graduate of Trinity College, University of Limerick and DCU.
Her first formal link to politics was as a consultant and researcher with the Institute of European Affairs, a think tank run by Brendan Halligan, the former Labour TD.
In the late 1990s, she joined Fianna Fail in Dublin West, defecting to Sinn Fein shortly afterwards.
In 2002, Mrs McDonald was Sinn Fein’s candidate in Dublin West, but she failed to win a seat in the Dail.
But two years later, she made history by becoming the party’s first MEP.
By 2009, she was deputy leader of the party – and in 2011 became a member of the Dail for Dublin Central.
Her rapid rise through the Sinn Fein ranks will now see her become the first female leader of the republican party.
But it is set to become a baptism of fire with many difficult issues to be tackled, including a referendum on abortion in the Republic, ongoing Brexit negotiations and attempts to restore powersharing at Stormont.
Despite replacing one of the defining figures of the republican movement, Mrs McDonald has no intention of remaining in Mr Adams’ shadow.
In a speech when she became president-elect Mrs McDonald said she intend to walk in her own shoes.
“The truth is, my friends, I won’t fill Gerry’s shoes but the news is that I brought my own. So I will fill my shoes, I will walk in my shoes,” she said.