Montvila quickly established himself as one of the leading figures of the Lithuanian post-war avant-garde, embracing serial, aleatoric, twelve-tone, micropolyphonic, sonorist, and pointillist techniques.

[4] Montvila also composed the earliest surviving example of Lithuanian tape music: discovered in 2016, his Juodoji pantomima (Black Pantomime) likely dates from the early 1970s.

[5] Beginning in 1968, Montvila began corresponding with fellow modernist composers outside the Soviet Union including György Ligeti, Sylvano Bussotti, Karlheinz Stockhausen, György Kurtag, John Cage, Elliott Carter, Luigi Dallapiccola and Henri Pousseur, as well as Lithuanian expatriates Vytautas Bacevičius and Jeronimas Kačinskas.

[6][7] Despite his strong experimental leanings, Montvila based many of his compositions around Lithuanian folk music, which he began exploring after completing his conservatory education.

[8] His Gothic Poem for orchestra (1970) blends micropolyphony, Klangfarbenmelodie-like tone clusters, and melodies based on a pair of sutartinės, an ancient form of Lithuanian polyphonic vocal music.