Niall is a male given name of Gaelic origin, thought to mean "champion". It could also mean 'cloud' or 'passionate'.
Niall may also refer to:
- Niall of the Nine Hostages, High King of Ireland who lived in the early-to-mid 5th century AD
- Niall Caille mac Áeda, High King of Ireland in the 9th century AD
- Niall Quinn, Irish former international footballer and chairman of the English club Sunderland A.F.C.
- Niall Ferguson, Historian and the Laurence A. Tisch Professor of History at Harvard University
- Niall O'Brien (cricketer), Irish cricketer
- Niall Laverty, Irish mandolin virtuoso
- Niall Horan, one of the five-part boyband One Direction