Ostrovsky was born in the village of "Viliya" (today a village in Ostroh Raion, Rivne Oblast) in the Volhynian Governorate (Volhynia), then part of the Russian Empire, into a Ukrainian working-class family. He attended a parochial school until he was nine and was an honor student. In 1914, his family moved to the railroad town of Shepetivka (today in Khmelnytskyi Oblast) where Ostrovsky started working in the kitchens at the railroad station, a timber yard, then becoming a stoker's mate and then an electrician at the local power station. In 1917, at the age of thirteen he became a Bolshevik party activist. At the same period he contracted ankylosing spondylitis, which would later blind and paralyze him.