Events from the year 1858 in Ireland.

• 17 March – In Dublin, James Stephens founds the revolutionary organisation which becomes known as the Irish Republican Brotherhood.^[1][2]
• Edward Harland, at this time general manager, buys the small shipyard on Queen's Island, Belfast, from his employer Robert Hickson in conjunction with Gustav Wilhelm Wolff.^[3]
• Ballinacourty lighthouse at Dungarvan harbour built.

• First free public library in Ireland opens in Dundalk.

• 11 January – Mildred Anne Butler, painter (died 1941).
• 13 February – James Murray Irwin, British Army doctor (died 1938).
• 6 March – Coslett Herbert Waddell, priest and botanist (died 1919).
• 11 March – Tom Clarke, republican (born in England; executed 1916).
• 2 May – Edith Anna Somerville, novelist (died 1949).
• 19 May – Mike Cleary, boxer (died 1893).
• 5 October – Thomas Cusack, Democrat U.S. Representative from Illinois (died 1926).

  Full date unknown

  • Anne Marjorie Robinson, artist (died 1924).

• 4 March – John Ryan, soldier, recipient of the Victoria Cross for gallantry in 1857 at Lucknow, India, killed in action (born 1823).
• 26 April – Francis Murphy, first Roman Catholic bishop of Adelaide, South Australia (born 1795).
• 22 July – Mary Aikenhead, founder of the Sisters of Charity (born 1787).
• 28 July – Alexander Wright, soldier, recipient of the Victoria Cross for gallantry in 1855 at Sebastopol, in the Crimea (born 1826).
• 17 August – Robert Cane, doctor, member of the Repeal Association and the Irish Confederation, Mayor of Kilkenny (born 1807).

  Full date unknown

  • John Hogan, sculptor (born 1800).
  • Benjamin Lett, bomber and arsonist in America and Canada (born 1813).
  • James Roche Verling, British Army surgeon, became personal surgeon to Napoleon Bonaparte on St Helena (born 1787).

• 1858 in Scotland
• 1858 in Wales