Meagher’s story is extremely important in the origins of the Irish tricolour flag, because of his central role in promoting it during 1848, and his role in the 1848 rebellion, establishing its relationship with the idea of an Irish republic
Thomas Francis Meagher was an Irish revolutionary who was exiled from Ireland to Tasmania. He escaped and came to New York where he became a lawyer and made a famous effort in the United States Court, in the case of Fabens and other Nicaragua "filibusters." He conceived the idea of an expedition to Central America (taken with Don Ramon Paez, son of President Paez of Venezuela) and made a report on the feasibility of a canal through the isthmus by way of Nicaragua.
Meagher fought at the first battle of Bull Run (Manassas) as a captain of the Zouave Company in the 69th New York Militia. When he returned to New York he received permission to organize an Irish Brigade. The 69th New York Militia served as the nucleus for the Brigade and its 1st Regiment, the 69th New York Infantry Regiment.
Meagher was appointed Brigadier General and led the Irish Brigade during: the Peninsular Campaign, Mechanicsville, Fair Oaks, the Peach Orchard, Malvern Hill, Antietam, Fredericksburg, and Chancellorsville. After the Civil War he became the acting Governor of Montana.