He was an avid swimmer throughout his life, taught early on by Duke Kahamamoku, where learned the breath control that later served him well as a professional flutist.

[5] In 1911, Kincaid moved to New York, enrolling in Columbia University and the (now the Juilliard School), where he studied flute with Georges Barrère.

[5] During World War I, Kincaid served briefly in the United States Navy, later rejoining the New York Symphony.

[7] After André Maquarre was dismissed by Leopold Stokowski in April 1921 during a rehearsal, Kincaid was offered the principal flute position in the Philadelphia Orchestra, which he went on to hold for 40 seasons.

In either 1924 or 1928 (sources vary), Kincaid joined the faculty of the newly established Curtis Institute of Music, where his four decades of teaching would have a profound impact on orchestral flute playing in the United States.

[16] Through the work of Demetra Fair at the Ohio State University during her dissertation writing, an extensive research study of 4,360 American flutists and their "flute" lineage, it became clear that William Kincaid, George Laurent and Marcel Moyse form the basis of the American Flute School.