Donnelly is an Irish surname. It is the Anglicized form of the Gaelic "Ó Donnghaile", "Ó" meaning male descendant of ("Ní" is the female equivalent), and Donnghaile (or Donnghal), a personal name composed of the elements "donn" (brown), plus "gal" (valour). The name O’Donnelly is derived from the descendants of Donnghaile (Donnghal) (an individual who lived during 10th century in Ireland) who was the great grandson of Domhnall, King of Aileach. Early ancestors of this surname were a part of Cenél nEoghain and the Uí Néill as descendants from the line of Eógan mac Néill one of the seven sons of Niall Noígíallach (an Irish king).
It is most commonly found in County Tyrone in mid- and west Ulster. It was so common in Roscommon that at some point, a branch of people with the Donnelly surname took on the name of Briscoe instead.
A major stronghold of the (O')Donnelly family was located in Ballydonnelly, today known as Castlecaulfield, United Kingdom. The castle is called both Castle Caulfield and Ballydonnelly, dependent on who one asks. The land in this area traded hands a few times. Toby Caulfield, 1st Baron Caulfeild built a castle where an O'Donnelly residence stood between 1611 and 1619 when he acquired 1,000 acres of the Earls of Tyrone's estates. Patrick Donnelly burned the castle during the Irish Rebellion of 1641. In the 1660s, the Caulfield family was able to restore and re-occupy said castle. Oliver Plunkett and John Wesley both held services in the castle in 1670 and 1767, respectively. However, the castle fell into disrepair around the year 1700. Today, the castle is a State Care Historic Monument in County Tyrone.
- Alan Donnelly (born 1957), British politician and former trade unionist
- Arthur Barrett Donnelly (1875–1919), US Army general
- Brendan Donnelly (born 1950), British politician
- Brendan Donnelly (born 1971), baseball player
- Brian Donnelly (disambiguation)
- Charles Donnelly (disambiguation)
- Charley Donnelly (1885–1967), American educator, golfer, and football and golf coach
- Ciaran Donnelly (born 1984), English footballer
- Dan Donnelly (disambiguation)
- Davis A. Donnelly (1927–2020), Wisconsin senator
- Declan Donnelly (born 1975), English television presenter, producer and actor, one half of Ant & Dec
- Desmond Donnelly (1920–1974), British politician, author and journalist
- Dick Donnelly (1941–2016), Scottish football player, journalist and broadcaster
- Donal Donnelly (1931–2010), Irish theatre and film actor
- Dougie Donnelly (born 1953), Scottish television presenter
- Edward Terence Donnelly (1871–1929), US Army general
- Elfie Donnelly (born 1950), British-Austrian children books writer
- Fin Donnelly (born 1966), Canadian politician
- Gary Donnelly (born 1962), American tennis player
- Gary Donnelly, Irish republican
- Greg Donnelly, Australian politician
- Henry Edmund Donnelly (1904–1967), American Catholic bishop
- Ian Donnelly (1981), Australian rugby league footballer
- Ignatius L. Donnelly (1831–1901), Minnesota politician
- Jack Donnelly (born 1985), English actor
- James S. Donnelly Jr. (born 1943), historian
- Jamie Donnelly (born 1947), American actress
- Jason Donnelly (born 1970), New Zealand rugby league footballer
- Jennifer Donnelly (born 1963), American novelist
- Joe Donnelly (born 1955), American attorney and politician
- Joseph Francis Donnelly (1909–1977), American Catholic bishop
- John Donnelly (disambiguation)
- Ken Donnelly (born 1950–2017), American politician
- Liza Donnelly, American cartoonist and writer
- Luke Donnelly (born 1996), Scottish footballer
- Laura Donnelly (born 1982), Irish actress
- Malcolm Donnelly (born 1943), Australian baritone singer
- Mark Donnelly (born 1955), Professor, Publisher, Author
- Martin Donnelly (disambiguation)
- Mattie Donnelly, Irish Gaelic footballer
- Mattie Donnelly, Irish hurler
- Melinda Romero Donnelly (born 1971), Puerto Rico politician
- Michael Donnelly (1927–1982), Roman Catholic priest from Ireland
- Michael Donnelly (1959–2005), Gulf War veteran, activist, and author
- Mike Donnelly (born 1963), American hockey player
- Patrick Donnelly (disambiguation)
- Peter Donnelly (born 1959), Australian mathematician
- Peter F. Donnelly (1938–2009), American patron of the arts
- Phil M. Donnelly (1891–1961), Missouri governor 1945-49 and 1953–57
- Rich Donnelly (born 1946), American baseball coach
- Ruth Donnelly (1896–1982), American stage and film actress
- Ryann Donnelly, American musician
- Scott Donnelly (born 1987), English football player
- Scott C. Donnelly (born 1961), Chief Operating Officer of Textron
- Seamus Donnelly (disambiguation)
- Shannon Donnelly, Children's novelist
- Sharon Donnelly (born 1967), Canadian athlete
- Simon Donnelly (born 1971), Scottish footballer
- Tanya Donelly (born 1966), American musician
- Thomas Donnelly (politician) (Thomas F. Donnelly, 1874–1948), Canadian member of Parliament
- Thomas Donnelly (sergeant-at-arms) (1764–1835), New York legislative officer
- Thomas Donnelly (writer) (born 1953), American writer and director of the Center for Defense Studies at the American Enterprise Institute
- Thomas Charles Donnelly (born 1933), former Alberta MLA
- Thomas Dean Donnelly, American screenwriter
- Thomas F. Donnelly (New York City) (1863–1924), New York politician and judge
- Tom Donnelly (Thomas Mathew Donnelly, born 1981), New Zealand rugby union player
- Tom Donnelly (footballer) (born 1947), Scottish footballer for Motherwell and East Stirlingshire
- Tommy Donnelly (footballer), Irish association football player
- William Donnelly (disambiguation)
- The Black Donnellys, a feuding Canadian family
- Norman, Tess (2003). A World of Baby Names. Penguin. p. 286.
- "Last name: Donnelly". The Internet Surname Database.
- The most accurate source for the pedigree of Donnghaile (Donnelly) can be found in O’Cleary, Michael, et al, Annals of the Four Masters, see O‘Donovan‘s edition  Volume 6, page 2426. Other Irish genealogies (Book of Ballymote and Book of Lecan) have the line of descent of Donnghaile incorrectly stated as the great grandson of Domnall Ilchelgach, High King who died in 561 A.D.
- King Domhnall served as co-ruler of Cenél nEoghain from about 896 A.D. with his paternal half brother Niall Glundub until 911 A.D. when King Domhnall abdicated to “enter religious life” and subsequently died in 915 A.D. Hudson, Benjamin, Prophecy of Berchan,Irish and Scottish High Kings in the Middle Ages, Greenwood Press 1996 page 148.
- Kenny, Kevin (1998). Making Sense of the Molly Maguires. Oxford University Press. p. 300. ISBN 9780195116311.
- Radford, Dwight A.; Betit, Kyle J. (2012). A Genealogist's Guide to Discovering Your Irish Ancestors. Betterway Books. p. 12.
- "Castles.nl – Castle Caulfield". www.castles.nl. Retrieved 2020-04-12.
- "State Care Historic Monuments to 31 March 2007" (PDF). Retrieved April 12, 2020.