Gallagher is a common surname derived from the Irish name Ó Gallchobhair. In the United States, it was ranked by the 2000 U.S. Census as the 574th most common name out of over 80,000 surnames found.

The Gallagher coat of arms displays a spectacular roaring black lion, stepping on a violently green snake surrounded by eight trefoils. The family hails from County Donegal, Ireland.

The Gaelic meaning of the surname Gallagher is "Foreign Help" or "Foreign Helper". The name can be traced back to 5th century High King/Warlord "Niall Noigíallach" or Niall of the Nine Hostages.