Life

Donnchadh is almost wholly known from Araile do fhlathaibh Ua nDubhda, which says of him:

• Donnchadh Ó Dubhda [came] with a fleet
  Fleet
  -Vehicles:A fleet is a collection of ships or vehicles, with many specific connotations:*Fleet vehicles, two or more vehicles*Fishing fleet*Naval fleet, substantial group of warships*A group of small ships or flotilla...
  
   of fifty-six ships from Innse Gall and came ashore in Inis Raithin among Inse Modh in Umhall
  Umaill
  Umaill was a kingdom or territory located in the west of what is now County Mayo, Ireland. It comprmised of the baronies of Burrishoole and Murrisk, essentially all the land adjacent to Clew Bay.-Description:...
  
  , and he seized his own land free of tribute from Cathal Crobhdearg Ua Conchobair.

Genealogy

Dubhaltach Mac Fhirbhisigh

Dubhaltach Mac Fhirbhisigh

Dubhaltach MacFhirbhisigh, also known as Dubhaltach Óg mac Giolla Íosa Mór mac Dubhaltach Mór Mac Fhirbhisigh, Duald Mac Firbis, Dudly Ferbisie, and Dualdus Firbissius was an Irish scribe, translator, historian and genealogist...

 gives what appears to be his genealogy

Genealogy

Genealogy is the study of families and the tracing of their lineages and history. Genealogists use oral traditions, historical records, genetic analysis, and other records to obtain information about a family and to demonstrate kinship and pedigrees of its members...

 (265.2, pp. 598–99, volume I):

• Donnchadh Mór (mac Aodha m. Taithligh m. Aodha m. Muircheartaigh m. Aodha m. Taithligh m. Nell), trí mec les .i. Brían, Maolruanaidh, agus Muircheartach, ó ttaid Clann Chonchabhair/Donnchadh Mór (s. Aodh s. Taithleach s. Aodh s. Muircheartach s. Aodh s. Taithleach s. Niall) had three sons: Brian, Maol Ruanaidh, and Muircheartach, from whom are Clann Chonchabhair.

At 265.5 (pp. 600–601), Mac Fhirbhisigh gives the genealogy of another Donnchadh Mór, son of Taichleach O Dubhda, has having three sons; Donnchach Og, royal candidate of Ui Fhiachrach, Conchabhar, and Uilliam, bishop of Ceall Aladh (Kilalla), stating that the daughter of O Floinn was mother of those sons of Donnchadh Mor.