* In and Out of Harm's Way: U.S. Military Advisors in Northern Ireland
* Brothers on the Battlefield
* The Irish in the American Revolution
* All That I Have: The Life and Legacy of Reverend Charles T. "Doc" O'Hara, S.J.
* Through a Hell of Bullets: Combat Chronicles of the Irish Brigade
Articles and Chapters in Books
* "The IRA in the 1920s: Between War and Peace" in Rebels to Revolutionaries? Commemorations of the 1916 Rising in Ireland, 1926–2016, ed. Eamon Phoenix (Manchester University Press, 2020).
* "Irish Revolutionary Nationalism and the Irish Brigade, 1968–1982" in Transnational Irish Rebels: Networks of Support for the Republican Movement in the Late 20th Century, ed. Anthony McIntyre (Cork University Press, 2019).
* "In the Crucible of World War I: The Irish Volunteers, the Great War, and the Rise of Militant Republicanism" in In a Great Cause: Reflections on the Irish Revolutionary Period, ed. Eamon Phoenix (Irish Academic Press, 2017).
* "The Republican Movement and the Irish Brigade: A Question of Loyalty" in The Irish Revolution and International Relations, ed. Eunan O'Halpin and John M. Regan (Manchester University Press, 2016).
* "A War of Attrition: The IRA's Bombing War against Britain (1939-1945)" in Irish Guerrillas: Warfare, Resistance and the Irish State, ed. Brian Hanley and Scott Nelson (Oxford University Press, 2016).
* "From War to Peace: Irish Brigade Veterans and the Search for Stability" in The Dynamics of Decommissioning: Insights from Northern Ireland, ed. Brian Ó Cuív and John Darby (Ashgate, 2016).
* "The Irish Volunteers and the Home Rule Crisis, 1912-1914" in The Home Rule Crisis: The Fate of the Third Irish Home Rule Bill, 1912-1914, ed. Richard English and Graham Walker (Palgrave Macmillan, 2015).
* "In the Trenches of the Great War: Irishmen and the British Army" in The Long Shadow: Essays in Contemporary Irish History, ed. Eamon Phoenix (Irish Academic Press, 2015).
* "Rebels and Revolutionaries: The Irish Volunteers and the Easter Rising" in Rebels and Revolutionaries: The Dublin Rising and the First World War, ed. Paul Bew and John Horne (Oxford University Press, 2015).
* "Rebels and Rebellion: The Irish Volunteers, the Easter Rising, and the Fate of Irish Nationalism" in The Oxford Handbook of the Irish Revolution, ed. Fearghal McGarry and John Regan (Oxford University Press, 2014).
* "The Irish Brigade and the Long War: A History" (History Ireland, Volume 18, Issue 5, September/October 2010)
* "Beyond the Call of Duty: The Irish Volunteers and the Great War" (History Ireland, Volume 20, Issue 1, January/February 2012)
* "The Battle of Enniscorthy, 20-21 May 1798: A Rebel View" (Wexford Historical Journal, Volume 23, 1997)