William Masselos was born in Niagara Falls, New York to a Dutch mother and a Greek father.
[1] He studied with Carl Friedberg, a disciple of Johannes Brahms and Clara Schumann, and also with Nelly Reuschel (another Clara Schumann disciple) at New York's Institute of Musical Art (later called Juilliard School).
In 1952, at the age of 32, Masselos played the Brahms Piano Concerto in D minor in his first appearance with the New York Philharmonic Orchestra, led by Dimitri Mitropoulos.
Known as a champion of contemporary music, Masselos premiered many works including the Charles Ives Piano Sonata No.
He was the soloist in the first performances of piano concertos by Alan Hovhaness, Johan Franco, Marga Richter, Carlos Surinach, and William Mayer, in addition to solo pieces by John Cage, Dane Rudhyar, Robert Helps, Carlos Chávez, and many others.