Pustoviit worked in the fields of book and easel graphics, posters, and ex libris. His works were exhibited at all-Union and international exhibitions. He designed covers and illustrated publications, including The Cross-Paths and the historical tale Zakhar Berkut by Ivan Franko, The Hired Woman by Taras Shevchenko (1938), Stories by Mykhailo Kotsiubynskyi, the Ukrainian edition of Oblomov by Ivan Goncharov, All Quiet on the Western Front by Erich Maria Remarque, The Iron Heel by Jack London, collections of works by Andrii Malyshko, Maksym Rylskyi, and Mykhailo Stelmakh, the poem Danylo Halytskyi by Mykola Bazhan, among others.

In 1941, Havrylo Pustoviit was mobilized into the army. During the Second World War, he worked as a military journalist and headed the Union of Artists of Ukraine in evacuation. During these years, he depicted destroyed cities and drew portraits of soldiers, as well as a gallery of portraits from life of Ukrainian cultural figures such as Oleksandr Dovzhenko, Andrii Malyshko, Volodymyr Sosiura, Yurii Yanovskyi, Wanda Wasilewska, and others.

In 1942, the artist was accused of nationalism and anti-Soviet agitation and sentenced to ten years of corrective labor in an NKVD camp in Astrakhan. While imprisoned, Pustoviit fell ill with tuberculosis, and in the fall of 1943 he was released as terminally ill, without the right to return to Ukraine. After his demobilization in the summer of 1945, he underwent treatment in hospitals in Stalingrad, Moscow, and Kyiv. Pustoviit was posthumously rehabilitated in 1956 for lack of evidence of a crime.

The works of Havrylo Pustoviit are preserved in the National Art Museum of Ukraine, the National Museum of Taras Shevchenko, the Shevchenko National Reserve in Kaniv, the National Museum of Literature of Ukraine, as well as in other museum and private collections worldwide.