milne-thomson was born in ealing, london, england on 1 may 1891 to colonel alexander milne-thomson, a physician and eva mary milne, the daughter of the revd j. milne. he was the eldest of his parents' sons. he studied at clifton college in bristol as a classical scholar for three years. after securing a scholarship, milne-thomson joined corpus christi college, cambridge in 1909 and received part i of the mathematical tripos in 1911. he graduated with distinction as a wrangler in 1913.