Having been educated at Merchant Taylors School, London, from 1882 to 1887, Collett began his engineering career as a pupil of of Joshua Field of Maudslay, Son & Field. Eventually, in 1893, he joined GWR working initially as a draughtsman in Swindon. After a series of promotions he eventually suceeded George Jackson Churchward as Chief Mechanical Engineer at GWR, in 1922. He retired from GWR in 1941, at the age of 70.