 His education, in two local schools, was rudimentary and at the age of fifteen he started working as an apprentice carpenter in the Brewery.His apprenticeship involved learning to make office furniture and attending evening classes in nearby colleges, where he was able to improve his education in a more congenial atmosphere.A love of music and the arts had been encouraged by two maiden aunts – his parents subsequently bought an upright piano and he learned to play it at the Read Pianoforte School – and consequently, when his apprenticeship was completed and he was on the dole for some years, he spent much of his spare time buying pictures, books, antiques and old clocks and watches in the various auction rooms and antique shops in Dublin

During the mid-1930s, Gannon became a member of several Dublin-based societies, most notably the Old Dublin Society, and there befriended well-known people such as Grace Plunkett (née Gifford), the widow of Joseph Mary Plunkett (who had been executed after the Easter Rising of 1916).