In the field of research she focused on the musical history and musical historiography of Slovakia, fundamental research of sources for the history of Slovak music with regard to the renaissance and baroque periods, from the 1950s and ’60s with emphasis on the new musico-historical research (field research, catalogisation and transcription work).
She discovered precious manuscripts in Štítnik, works by the Franciscan musicians Jozef Pantaleon Roškovský and Edmund Pascha, and processed the effects of Mikuláš Schneider-Trnavský. Co-author of the script for the permanent exhibition in the Mikuláš Schneider-Trnavský House of Music in Trnava, she wrote the catalogue of the Levoča collection and also entries in the Encyklopédia Slovenska. She produced monographic studies on the Franciscans and dance music in Slovakia in the 17th and 18th centuries. Articles of hers were published on opera performances and organ concerts.
Mária Jana Terrayová also addressed the issue of the revival of historical Slovak music. She collaborated in six gramophone recordings with leading Slovak and Czech performers for Supraphon and Opus and eleven TV and short films and radio broadcasts. Certain works from Slovak musical history became hits, e.g. Vesperae Bacchanales by the late baroque Slovak composer Jozef Pantaleon Roškovský, Vianočná omša F dur (Christmas Mass in F Major – Harmonia Pastoralis) by Fr. Juraj Zrunek, OFM, originally attributed to Edmund Pascha. She collaborated as dramaturge on the films Štítnicky objav (Dicovery on Štítnicky), directed by V. Andreánsky (1964) and Harmonia pastoralis, directed by Martin Ťapák (1970).