Because of other threads - Carrickfergus and McAlpine's Fusiliers I've been looking harder than usual at Dominic Behan's "Ireland Sings) (London, 1965). There is an introductory "Notes on some song makers of the past" which mentions Charles Graham Halpin -

This is a summary of what Behan wrote - it has not been checked:

Son of Rev Nicholas Halpin, who was editor of the Dublin Evening Mail for some time. Charles wrote for the "Boston Post" and then in New York for the Herald, the Times and the Tribune, edited (briefly) a periodical "The Carpet-Bag" in which he wrote satire. He became a lieutenant in the 69th Regiment of the Union army at the outbreak of the American Civil War, acted as adjutant to General Halleck, ended the war as a Brigadier-General. Afterwards he had great influence in the Democratic Party and had a hand (perhaps a leading hand) in cleaning up Tamany Hall. He wrote also "Not a star from the flag shall fade" as a song for his regiment.