Events from the year 1790 in Ireland.

• Monarch: George III

• 15 March – The Sick and Indigent Roomkeepers' Society is established in Dublin; by the 21st century this will be the city's oldest surviving charity.^[1]
• May – construction begins on the Royal Canal at Cross Guns Bridge in Phibsborough, Dublin.^[2]
• Armagh Observatory, founded by Richard Robinson, 1st Baron Rokeby, Archbishop of Armagh, begins to function.

• Emo Court, near Emo, County Laois, is designed by James Gandon for John Dawson, 1st Earl of Portarlington.

• 1 January – George Petrie, painter, musician, antiquary and archaeologist (died 1866).
• 15 April – Theobald Jones, British Royal Navy officer, lichenologist and Unionist politician (died 1868).
• June – Arthur Jacob, ophthalmologist (died 1874).
• 10 October – Father Theobald Mathew, temperance reformer (died 1856).
• Alexander Pearce, transported convict and cannibal (executed 1824 in Van Diemen's Land).

• Patrick Browne, physician and botanist (born 1720).