Republican Solipsist discusses the life of Joseph McGarrity and his role within Irish and Irish American Republicanism including the complicated transatlantic relationship between two opposing visions of an independent Ireland. McGarrity's militant Republicanism came into regular conflict with the reality of the political situation in Ireland.

While the role of John Devoy has been well documented in the development of Irish American nationalism in the form of Clan na Gael that of Joseph McGarrity has been less well analyzed. For many historians the central focus of Irish American nationalism during the revolutionary period of 1916–1923 has centered on the Devoycontrolled branch of Clan na Gael. However, this period saw significant influence from McGarrity and the Philadelphia branch of the movement in shaping political events in Ireland which has been largely ignored.

The book places McGarrity at the center of Irish Republicanism during one of the most critical periods of its history. It is hard to imagine how militant Irish Republicanism would have evolved had it not been for the role and influence of this long-neglected figure in Irish history.