Kroyt was born to a Jewish-Ukrainian family in Odessa, but spent his early life and career in Germany where he had been a child prodigy violinist.

From the outbreak of World War II until his death at the age of 72, he lived in the United States and had become a naturalized U.S. citizen in 1944.

He later bought Kroyt his first real violin and persuaded a violinist friend of his to give the child proper lessons.

[4] Kroyt's mother was initially opposed to her son becoming a musician, but on the advice of the violin virtuoso Alexander Fiedemann who had heard Boris playing a Haydn string trio with two other children, she eventually relented and enrolled him at the Imperial Music College of Odessa.

[5][4] After his graduation from the Stern Conservatory, Kroyt embarked on an international concert career as a violinist, playing in solo recitals and violin concertos, and with string quartets.

In 1924 Kroyt played in the first post-World War I performance of Schoenberg's Pierrot Lunaire in an ensemble that included Schnabel, the cellist Gregor Piatigorsky and the soprano Marie Gutheil-Schoder.

To supplement his meager earnings as a classical musician in the 1920s, Kroyt also played jazz in the Ruscho and Tariffa cafés in Berlin and led a small orchestra that performed and recorded tango music and operetta tunes.

In May 1936 he accepted an offer to play in an orchestra in Tel Aviv that was being formed by William Steinberg and Bronisław Huberman.

However, later that month his old friend Josef Roisman (1900–1974), who was the First Violin for the Budapest String Quartet, asked him to replace their recently resigned violist István Ipolyi [it].

Reluctant to move his young family to Palestine and an uncertain future and seeing the large number of international concerts for which the quartet were contracted, Kroyt accepted Roisman's offer.

The Kroyt family settled in a house in Northwest Washington, D.C. where they became known for their soirées which were attended by prominent musicians and political figures.

[4][1][9][10] The music critic Michael Steinberg recalled meeting Kroyt in Buffalo the previous year: It was an evening that ended with the Kroyts driving us to our hotel in an absolutely awesome vehicle, about the size of a motor launch, furnished in rich blues, frighteningly quiet, and representing a life style I had not associated with the playing of chamber music.

I remember, too, a man of rare warmth, charm and humor, who spoke generously, perceptively, and with pleasing irreverence, about his colleagues in the musical world.

The Guarneri Quartet played at his funeral, and a few days later at his recital in Pittsburgh, Perahia dedicated a Bach sarabande to Kroyt's memory .

He and Yanna also co-authored In the Shadow of the Civil War: Passmore Williamson and the Rescue of Jane Johnson published by University of South Carolina Press in 2007.

Their son Anthony Brandt is a composer and Professor of Composition and Theory at Rice University's Shepherd School of Music.