He is best known for his coverage of the Russo-Ukrainian War in 2014 and 2015, when he was dispatched by VICE News to cover the events that unfolded in Ukraine as the country came into conflict with neighbouring Russia prior to and after Crimea's annexation by the latter.

[5][non-primary source needed] Ostrovsky traced the supply chains of multinational garment retailers like Topshop, Walmart and H&M to Uzbekistan, leading many Western cotton buyers to eventually boycott the country.

In a report for the UK's Independent newspaper he described how a "North Korean labour force tens-of-thousands strong, put in place across Asia," helped finance the regime in Pyongyang through contracts with Western firms.

"[11] In early 2014, he helped launch the company's new current affairs division, VICE News, with his investigation into allegations of corruption at the 2014 Winter Olympics in Sochi[12] and coverage of the 2014 crisis in Ukraine.

His series of unvarnished video dispatches from Ukraine titled "Russian Roulette"[13] won VICE News widespread acclaim and recognition as a burgeoning player on the media landscape.

[18][19] On April 21, 2014, while producing "Russian Roulette", a series of reports for Vice News in eastern Ukraine, Ostrovsky's vehicle was stopped at a separatist checkpoint in the city of Sloviansk.

Immediately prior to his detention, Ostrovsky had been investigating Russian citizens' involvement in the pro-Russia armed groups of eastern Ukraine, something separatist forces were trying to hide at that early stage of the conflict, according to a video deposition he made for VICE News following his release.

[24] The security situation around Sloviansk had begun to deteriorate, as Ukrainian forces reached the outskirts of the city and began engaging separatist units with armoured vehicles.