He was a teacher when his talent was discovered. He studied with Bertalan Székely at the Apprentice School of Decorative Arts and then in Munich, where he won a number prizes at the Academy. Scholarships also made it possible for him to attend the Julian Academy in Paris from 1900 and to go to Italy in 1902. Returning to his birthplace, he settled in the county of Csik in Transylvania and began to work near Lake Gyilkos. He served in the First World War and though not an official war painter, he made numerous drawings on the front, mostly portraits of soldiers. After the war, he lived in Transylvania for a short time, moving on to Budapest and also spending a spell of time with his friend József Koszta near Szentes. He returned to work in Transylvania in the second half of the twenties, also showing his work there. He travelled all through Hungary and was for a time in Yugoslavia until illness forced him to settle down in 1930 in Baja. KUT elected him to core membership in 1936.
Bibliography: Surányi, Miklós: Nagy István, Budapest, Singer és Wolfner, 1923. o Lyka, Károly: Nagy István, Budapest, Uj Idők, 1944. o Pap, Gábor: Nagy István, 1873-1937, (A Művészet Kiskönyvtára, 70), Budapest, Corvina, 1965. o Emlékkiállítás Nagy István festőművész születésének 100. évfordulója tiszteletére, (exhibition: Marosvásárhely, Művészeti Múzeum, 1973), ed. Simon Endre, Marosvásárhely, 1973. o Solymár István: Nagy István, Budapest, Képzőművészeti Alap, 1977. o Murádin Jenő: Nagy István, Bukarest, Kriterion, 1984.