From Wikipedia; "Johnny I Hardly Knew Ye" is a popular traditional song, sung to the same tune as "When Johnny Comes Marching Home". First published in London in 1867 and written by Joseph B. Geoghegan, a prolific English songwriter and successful music hall figure (Lighter 2012, pp. 28 – 29).

From FOLK SONG AND MUSIC HALL The intersection of folk and music hall, the songs and social history; [Joseph Bryan (Jack) Geoghegan (1816-89)] was born in Barton-upon-Irwell (part of Salford) in 1816, son of a fustian cutter from Dublin, his mother was from Manchester. Allegedly “before he reached manhood [he] took to writing songs upon current events”. Steve Gardham and others active on Mudcat have found around 300 songs written by Geoghegan.

Jack didn’t live by the standards of the day! He married Elizabeth in 1833 and went on to have nine children with her. But he also started a second family with Mary Birchall around 1850 and went on to have eleven children with her. He maintained the two the two families simultaneously, until Elizabeth died in 1871, and he very soon after married Mary.

Geoghegan worked at the Star Hotel in Liverpool from 1845 to 1858, may have been based in Glasgow 1859-1860, worked in several music halls in Sheffield from 1860 to 1864, before becoming the chairman of ceremonies at the Bolton Museum and Star Music Hall in the late 1860s and 1870s.