In Connacht, Munster and Leinster, the name is usually spelled with an "e" on the end. It is Norman in origin. A Le Brun came from Normandy and settled in Co Galway in the 12th century. An even earlier Browne, Sir Philip Browne, had arrived with the Anglo-Norman invasion in 1170 and become Governor of Wexford. The name can also be traced back to the Old English "Brun", which referred to hair, clothes or complexion. In Ulster, Brown is usually spelled without the "e" and its origins there are quite different. This name is an anglicisation of the Scots Gaelic, Mac a' Bhruithin (son of the judge) or Mac Gille Dhuinn (son of the brown boy).

Among the well-known Browns was William Brown, born in Foxford, Co Mayo in 1777. In 1813, he became closely involved with the struggle for Argentinian independence and is regarded as the father of the Argentinian navy. He is duly commemorated in his native Foxford, and in central Buenos Aires the main square is called Plaza del Mayo, after his native county.