In 1938 he wrote the soundtrack of the film Senderos de Santa Fe and met showbiz figures such as composer Valdo Sciammarella and playwright Alberto Vaccarezza, who helped him become lead pianist with Francisco Canaro's orchestra in 1939.

Together with Enrique Santos Discépolo, he authored such classics as Uno (1943),[4] Sin palabras (1946)[5] and Cafetín de Buenos Aires (1948).

[6] Mores and José María Contursi wrote En esta tarde gris (1941), Tu piel de jazmín (1941), Grisel (1942) and Cristal (1944).

Mariano Mores took part in several musical films together with such stars as Delia Garcés, Osvaldo Miranda, Virginia Luque and Hugo del Carril.

Mores created the modern tango sextet (organ, piano, bandoneon, electric guitar, keyboard, drums and bass) and established himself as one of the leading figures of the Argentine popular music.