Events from the year 1780 in Ireland.

• Monarch: George III

• August – passenger boat service begins on Grand Canal between Dublin and Sallins.^[1]
• Sacramental Test abolished.^[2]
• Henry Grattan demands parliamentary independence.^[2]
• Lady Berry, sentenced to death for the murder of her son, is released when she agrees to become an executioner (retires 1810).
• The model cotton manufacturing town of Prosperous, County Kildare, developed by Robert Brooke (East India Company officer), begins to function.
• The whiskey company John Jameson is established.

• January – William Henry Fitton, geologist (died 1861).
• 12 March – David Barry, military surgeon and physiologist (died 1835).
• 20 March – Myles Byrne, a leader of the Irish Rebellion of 1798 and soldier in the service of France (died 1862).
• 13 April – Alexander Mitchell, engineer and inventor of the screw-pile lighthouse (died 1868).
• May – Amhlaoibh Ó Súilleabháin, author, teacher, draper and politician (died 1838).
• 17 August – George Croly, poet, novelist, historian and divine (died 1860).
• 1 December – Edward Bowen, lawyer and politician in Lower Canada (died 1866).
• 20 December – John Wilson Croker, statesman and author (died 1857).

• Full date unknown

  • Michael John Brenan, priest and ecclesiastical historian (died 1847).
  • Thady Connellan, schoolteacher and writer (died 1854).
  • Anne Devlin, republican and housekeeper to Robert Emmet (died 1851).

• 2 February – Thomas Waite, civil servant (born 1718).
• 3 June – Henry Denny Denson, soldier and politician in Nova Scotia (born c.1715).
• 25 August – William Bowles, naturalist (born 1705).
• October (drowned at sea) – Robert Boyle-Walsingham, British Royal Navy officer and politician (born 1736).
• 19 November – Jocelyn Deane, politician (born 1749).