He was adjutant-general of New York state in 1839-1843, and became a brigadier-general of volunteers in the Union army in 1861, commanded a division in Virginia in 1862-1863, and, being compelled by ill health to resign from the army, was U.S. minister to the Papal States in 1863-1867.
For his services at Franklin he was awarded the rank of brigadier-general (November 1864) and the brevet rank of major-general (March 1865) in the regular army.
In 1861 he was captain of a company (which he had raised) in the 69th regiment of New York volunteers and fought at the first battle of Bull Run; he then organized an Irish brigade, of whose first regiment he was colonel until the 3rd of February 1862, when he was appointed to the command of this organization with the rank of brigadier-general.
Lyons, in Brigadier-General Thomas Francis Meagher (New York, 1870), gives a eulogistic account of his career.
In the Civil War he attained the rank of brigadier-general (March 1863) and received the brevet of major-general (1865).
