In 1927, while still living in Florida, his mother took him to New York City to play for pianist Josef Hofmann, then Director of the Curtis Institute in Philadelphia.
At the first lesson, when it became clear that the young boy lacked proficiency in reading music, Saperton demanded an explanation, given that Foster had played Beethoven's Pathetique Sonata for Josef Hofmann months before.
In 1938, Foster won the MacDowell Competition, and in October 1940 his winning of the Edgar M. Leventritt Prize led to his debut with the New York Philharmonic Orchestra at Carnegie Hall under John Barbirolli.
"[4] A few months later, Foster made his New York recital debut in Carnegie Hall, with "pianism that was thrillingly alive and facile...taking rhythmic and dynamic liberties, sometimes very daring for a youthful artist, but which most often evidenced a remarkable feeling for striking effect.".
In 1955, in the hours following a recital in Racine, Wisconsin, Foster suffered a significant heart attack, which required prolonged hospitalization and which kept him from concert stages for over two years.
For several years he was joined on the Indiana University faculty by his childhood friends—and Curtis Institute classmates—concert pianists Abbey Simon and Jorge Bolet.
In 1972 the three gave solo recitals on successive weeks in Lincoln Center's Tully Hall to benefit the Indiana University Music School Scholarship Fund.
Despite the gradual toll it took—with weakness, discomfort, difficulty sleeping and increasing, but reasonably well disguised, frailty—Foster kept the diagnosis solely within his immediate family, continuing to concertize, performing his teaching duties at Indiana University, carrying a full load of students every semester, until his passing.
"[18] His recorded legacy includes two discs for the Musical Heritage Society: one features two Mozart Concerti with the Vienna Chamber Orchestra under Helmuth Froschauer, and the other, Opus 36-38 Clementi Sonatinas.
In 1993, the International Piano Archives at Maryland published a two-CD album, "Ovation to Sidney Foster," with several live performances from his recitals at Indiana University.
David Dubal, referring to Foster's performances of Mendelssohn's Three Etudes, Opus 104, and Prokofieff's Third Sonata in this album, called them "essential recordings of American pianism".
[20] In December 2018, a 7-CD set of live Sidney Foster recital and concerti performances, Rediscovering an American Master, was released by Marston Records.