[1] After schooling at the Birkenhead Institute, he proceeded to Trinity College, Cambridge, as a history scholar, and with the outbreak of the Second World War he joined the Royal Tank Regiment, eventually serving in Italy, Greece, and North Africa.
[2] Gallagher's influential work Africa and the Victorians: The Official Mind of Imperialism,[3] was co-authored with Ronald Robinson (with the help of Alice Denny) and first published in 1961.
In addition to being one of the most prominent theorists of imperial expansion, he also ensured a considerable legacy as a result of the large numbers of doctoral students at both Cambridge and Oxford whose work he either supervised or strongly influenced.
[7] Gallagher was strongly-left wing in his youth, and whilst an undergraduate at Cambridge he was a convenor of the 'colonial group' of the university's Communist Party.
The historian Eric Hobsbawm, a fellow student communist, described Gallagher as "brilliant, original and self-destructive", claiming that he never got out of bed before midday.