Byrne

The most common meaning of Byrne (variations: Burns, Byrn, Byrnes, O'Byrne) is a surname derived from the Irish name Ó Broin.
There are two Irish surnames which have Byrne as their English spelling; the most common comes from Ó Broin, which refers to the Leinster-based family of Bran as described below, the less common family name is Ó Beirn or Ó Beirne in Irish comes from a different Sept or family and therefore has different origins. The latter is most commonly found in Mayo, Sligo and Donegal in the Northwest of Ireland.
History.
In the Irish language, "Ó Broin" means "descendant of Bran". The name has been traced back to the ancient Celtic chieftain, Bran mac Máelmórda, King of Leinster, deposed in 1018, (d. 1052), who belonged to the Uí Dúnlainge dynasty. He was descended from Cathair Mór, an earlier king of Leinster, who was, according to medieval Irish legend and historical tradition, also monarch of all Ireland around 200 AD. The clan's motto is the Latin phrase "Certavi et vici", meaning "I have fought and conquered".
In pre-Norman times the O'Byrnes, then known as the Uí Fáeláin sept, inhabited the rich Kildare plains. With the progress of the Anglo-Norman conquest, they were compelled to migrate to the poorer lands and the mountainous country eastwards, later to be denominated as the county of Wicklow.