Johnnie was the eldest child of Angus MacKillop and Effie Munro of Baile, and later of 13 Borve, which his father was assigned in 1900. Johnnie was a pupil at Berneray School between 1903 and 1912.

He fought in the Great War, a private in the 2nd/4th Battalion, Oxford and Buckinghamshire Light Infantry. He was killed near Merville, France in 1918. His youngest brother, born a few months later, was also named Johnnie.