Niall Ó Donnghaile was born in Belfast in 1985. He graduated in politics from the University of Ulster and worked as Sinn Féin's director of communications at the Northern Ireland Assembly.

Ó Donnghaile was elected to Belfast City Council for Pottinger ward in May 2011, representing Sinn Féin. He became Lord Mayor in June 2011, and is the youngest ever Lord Mayor of Belfast. He served on Council until 2016.

In 2016 Ó Donnghaile was elected as a Senator to Seanad Éireann (Senate of Ireland), the upper house of the Oireachtas (Irish parliament).