Factbox-Michelle O'Neill, Northern Ireland's incoming first minister

BELFAST (Reuters) - Michelle O'Neill will become the new leader of Northern Ireland's regional government on Saturday, the most significant milestone yet in the shift to a new generation of Irish nationalists not directly involved in the region's decades-long bloody conflict.

- O'Neill, 47, represents Sinn Fein, the former political wing of the Irish Republican Army (IRA), which campaigns on both sides of the Irish border for an end to British rule in Northern Ireland and the creation of a united Ireland.

- Her formal appointment as first minister of Northern Ireland will end a long wait since Sinn Fein's unprecedented May 2022 electoral victory, and comes after the British government struck a deal this week with the pro-British Democratic Unionist Party (DUP), whose assent is required under the region's power-sharing arrangements.

- O'Neill began her political career aged 21 as an adviser at the Northern Ireland assembly in 1998, the year of the Good Friday peace agreement which largely ended the violent conflict between Catholic Irish nationalists and Protestant unionists.

- Her father was jailed during the conflict and later became a Sinn Fein councillor. Having followed her father into elected politics, O'Neill became the first woman to serve as mayor of her local council area. She was first elected to the Northern Ireland assembly in 2007.

- O'Neill became a mother aged 16. She has spoken of the difficulties of raising her daughter, Saoirse, in the Catholic community in 1990s Northern Ireland while still at school.

"You were neatly put in a box: single mother, unmarried mother, nearly written off," she said in a 2022 Sky News interview. "But I was determined that I wasn't going to be written off, that I was going to work hard and make a good life for her."

She also has a son, and in 2023 became a grandmother.

- Although seen as the face of a new generation of Sinn Fein, O'Neill worked alongside Martin McGuinness, the Irish Republican Army commander who became a cornerstone of Northern Ireland's peace.

McGuinness appointed O'Neill to the Northern Ireland Executive in 2011 and identified her as a potential leader before his death in 2017.

She helped carry McGuinness's coffin at his funeral.

- O'Neill attended both the funeral of Queen Elizabeth and the coronation of King Charles.

"We have bridges to mend and I look forward to working with King Charles. I'm sure that he will carry on the legacy of building relationships between our two islands," O'Neill said at the Queen's 2022 funeral.

(Reporting by William James and Amanda Ferguson; Editing by Nick Macfie)