The Irish sept Mac Donnchadha, provides the origin of the McDonaghs, McDonoughs, Donoghs, and Donaghys.
The Mac Donnchadha were kings and chiefs of the túath of Tír Olliol, now the barony of Tirreril in Co. Sligo, where they were a branch of the Mac Dermots. The name also arose in Co. Cork where it was located in the Barony of Dunhallow, as a branch of the powerful McCarthys. They were known as the "Lords of Dunhallow, their stronghold was actually in Kanturk.
The name today is found in its greatest numbers in Connacht, in particular, Co. Galway
"Son of Donagh - or Brown one"
VIRTUTIS GLORIA MERCES "Glory is the reward of valour".
||Bean Mhic Dhonnchadha
- Brendan McDonagh is the Managing Director of the National Asset Management Agency in Ireland.
- Charlotte McDonagh (1984 in Edgware, London, England), is a British actress.
- Donagh MacDonagh (1912–1968), Irish writer and judge (son of Thomas below).
- Eileen MacDonagh, Irish sculptor, active from the 1980s.
- Enda McDonagh is a priest of the Roman Catholic Archdiocese of Tuam.
- Jacko McDonagh (1962, Dublin), was an Irish professional footballer.
- Jarlath McDonagh (1945), is a Fine Gael politician from County Galway in Ireland.
- Jay McDonagh (born 1973), American football player
- Jim McDonagh (1952, Rotherham, England), nicknamed Seamus, is currently goalkeeping coach at Aston Villa.
- Joe McDonagh (1953, Ballinderreen, County Galway), is a retired Irish sportsman
- John MacDonagh (1880–1961) was an Irish film director (brother of Thomas MacDonagh)
- John Alfred Terence MacDonagh (3 February 1908 – 12 September 1986) English Oboeist. (Nephew of Thomas MacDonagh).
- John Michael McDonagh (1967) is a contemporary English-born Irish screenwriter and film director.
- Joseph MacDonagh (died 1922), Irish Sinn Féin politician (brother of Thomas).
- Maitland McDonagh, is an American film critic and the author of several books about cinema.
- Margaret McDonagh, Baroness McDonagh, is a British Labour Party politician and was General Secretary of the Labour Party from 1998 to 2001 (sister of Siobhain).
- Martin McDonagh (1970) is a contemporary English-born Irish playwright and film director.
- Michael McDonagh (1925), is an Irish traveller and proud to be Irish
- Mike McDonagh is a humanitarian, and a senior United Nations official working for the United Nations Office for the Coordination of Humanitarian Affairs.
- Monika MacDonagh-Pajerová (1966 - ), Czech academic.
- Mayor McDonagh The mayor of Diamond City who forced all non-feral ghouls out of the city
- Pat McDonagh is the founder of Supermac's.
- Paul McDonagh (1945), is a retired American professor and currently a senior amateur golfer in Tucson, Arizona.
- Peter McDonagh in Galway, Ireland is a professional boxer.
- Philip McDonagh is an Irish footballer currently playing for Bohemians in the League of Ireland.
- Ryan McDonagh (1989, Arden Hills, Minnesota) is a professional ice hockey defenceman.
- Siobhain McDonagh (1960, London), is a British Labour Member of Parliament for the Mitcham and Morden constituency in London (sister of Margaret).
- Stephen McDonagh (1970, Bruree, County Limerick), is a retired Irish sportsperson.
- Thomas MacDonagh (1878–1916), Irish nationalist poet, playwright, and a leader of the 1916 Easter Rising
- Willo McDonagh (1983, Dublin), is an Irish footballer currently playing for Glenavon F.C.