Mary Lou McDonald will succeed Gerry Adams as Sinn Fein leader, the party say, completing a generational shift for the Irish nationalist party as it bids to enter government on both sides of the Irish border.
Mr Adams, a pivotal figure in the political life of Ireland for almost 50 years, announced he would step down as leader of the former political wing of the Irish Republican Army (IRA) last November after more than three decades in charge.
Ms McDonald, who has been at the forefront of a new breed of Sinn Fein politicians softening the party's image, was the only person to put her name forward for the leadership.
"As we enter a new era, we look ahead with confidence as a party that is about being in government here in the north, in government in the south also, working forward all the time for the realisation of our ultimate goal of Irish unity," Ms McDonald said in a speech to party members in Belfast.
Mr Adams, still reviled by some sceptical voters as the face of the IRA during its campaign against British rule in Northern Ireland, hands over to a successor with no direct involvement in the three decades of conflict that came to an end in 1998.
It also means the left-wing party will be led on both sides of the border by women in their 40s after Michelle O'Neill succeeded Martin McGuinness as leader in Northern Ireland shortly before the former IRA commander's death in March.
Sinn Fein has shared power in Northern Ireland since 2007 and is in negotiations to try to restore the devolved executive there but it has never governed in the south.
While it trails the centre-right Fine Gael and Fianna Fail parties by some distance in opinion polls, recent surveys suggest some voters would be more willing to vote for a party led by Ms McDonald than Mr Adams.