Leo Berk was born in Belostok in Grodno Province (now Poland) and might have been of Belorussian or Jewish origin, but after his service in the Russian Army in the Russo-Japanese war he seems to have become Russianised and upon arrival to Brisbane in 1913 was a part of the Russian community there. He worked as a labourer in different parts of Queensland.
Enlisting in the AIF, he served as a gunner in the 4th Field Artillery Brigade on the Western Front. In May 1917 he was gassed and soon afterwards became sick and was evacuated to Australia.
During the Russian Revolution of 1917 he expressed more conservative positions and was at odds with the Russian community in Brisbane. Marrying a German woman, Margarite Stuewe in 1921, he moved to the Tumoulin – Ravenshoe area in North Queensland, working as labourer and millhand there and actively supporting the local RSSILA.