[3] His teaching career was interrupted by service in the Imperial Russian Army from 1914 to 1917.
In 1940, Puusepp was certified as a secondary and vocational school teacher of Estonian language and literature by the University of Tartu.
From 1946 to 1953 he taught in the Russian language department of the University of Tartu.
[2][3][5] Puusepp wrote 32 language textbooks for schools[2] with a combined print run of one million.
He prepared an extensive manuscript for his Vene-eesti fraseoloogilise sõnaraamatu (Russian–Estonian Phraseological Dictionary),[5] which, however, has not been published.