Born in London, Hallett left school aged fourteen.
He worked as a messenger before securing an apprenticeship as a fitter and turner in Beckton.
In 1918, he enlisted in the 10th London Regiment, but with World War I about to finish, he was discharged the following year.
He returned to employment as a fitter and turner, and became active in the Amalgamated Engineering Union (AEU).
[1] In his spare time, Hallett enjoyed long-distance running and race walking, and represented Essex in both events.