Shevelov prepared and published more than 600 scholarly texts concerning different aspects of the philology of the Ukrainian and other Slavic languages. From 1943 he developed the concept of the distinct establishment and development of Ukrainian and, later, Belarusian languages. Shevelov argued against the commonly held view of an original, unified East Slavic language from which Ukrainian, Belarusian and Russian languages diverged and instead proposed the existence of several dialectical groups (Kyivan-Polissyan, Galician-Podillian, Polotsk-Smolensk, Novgorodian-Tversk, Murom-Ryazansk) that had been distinct from the beginning and which later formed into separate Ukrainian, Russian and Belarusian languages.