Sir Roger O'Shaughnessy, The O'Shaughnessy (died 11 July 1690), was Chief of the Name and a Captain in the Irish army of James II of England. He was present at the Battle of the Boyne, dying ten days after at his castle in Gort. All his property was declared forfeit, and his son and heir, William O'Shaughnessy, was forced into exile. In 1697 Roger's estates were granted to Sir Thomas Prendergast, 1st Baronet, and the O'Shaughnessy family were never able to recover them.
Roger was the son of Dermot O'Shaughnessy.
He married Helena, daughter of Conor O'Brien, a son of Donogh O'Brien, 4th Earl of Thomond. Her brother was William O'Brien.
Their children were:
- Helena. She married Theobald Butler. They had three children: Francis, John and Theobald.
- Major General William O'Shaughnessy, The O'Shaughnessy.
Roger O'Shaughnessy succeeded to the O'Shaugnessy lands in Ireland in 1678. 
- O'Donovan, John. The Genealogies, Tribes, and Customs of Hy-Fiachrach. Dublin: Irish Archaeological Society. 1844. Pedigree of O'Shaughnessy: pp. 372–91.
- Lough Cutra, Galway, Castles in Ireland
- D'Alton, John, Illustrations, Historical and Genealogical, of King James's Irish Army List (1689). Dublin: 1st edition (single volume), 1855. pp. 328–32.
- O'Hart, John, Irish Pedigrees. Dublin: James Duffy and Co. 5th edition, 1892. pp. 754–6
- History of Galway, James Hardiman, 1820
- Tabular pedigrees of O'Shaughnessy of Gort (1543–1783), Martin J. Blake, Journal of the Galway Archaeological and Historical Society, vi (1909–10), p. 64; vii (1911–12), p. 53.
- Old Galway, Professor Mary Donovan O'Sullivan, 1942
- Galway: Town and Gown, edited Moran et al., 1984
- Galway: History and Society, 1996
Dermott Ó Seachnasaigh
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