By age 20, he had performed the Concierto de Aranjuez and Fantasia para un gentilhombre by Joaquín Rodrigo, and Concerto by Heitor Villa-Lobos – all with orchestra; and later also Concerto del Sur by Manuel María Ponce and Guitar Concerto, Op. 36 by Mauro Giuliani. By 25, he had won prizes in about 40 guitar competitions, such as Grand Prize at Ex-Aequo International Classical Guitar Competition, New York, in 2020, Special Prize for the Best Interpretation of Contemporary Music at Forum Gitarre, Vienna, in 2019.
Marcin Kuźniar has a strong interest in performing the works of contemporary composers not often heard in guitar recitals, such as Tristram Cary and Tristan Murail. His debut CD of 2018, Song Without Words, includes works by Richard Rodney Bennett, Alan Rawsthorne and György Ligeti complemented with a transcription of Moments musicaux by Schubert (rarely performed on guitar), and music by Mertz and Tárrega/Arcas. During 2020, he released videos of Escarraman by Mario Castelnuovo-Tedesco and Variations on a Theme of Debussy by Tilman Hoppstock, and began to transcribe music by Polish composers Penderecki, Weinberg, Szymanowski and Lutoslawski.