Throughout his career Loeffler claimed to have been born in Mulhouse, Alsace (i.e. to be basically a Frenchman), and almost all music encyclopedias give this fabricated information. In his lifetime articles were published dissecting his ‘typically Alsatian’ temperament! In fact he was German — indeed a Berliner on both sides of his family: he turned against Germany when the Prussian authorities imprisoned and apparently tortured his father, an agricultural chemist and author of Republican ideals. Loeffler was only about 12 when this happened; the father spent the rest of his life in prison, dying of a stroke before he was due to be released. Before this the family had moved around a good deal, including Alsace and then to Smiela near Kiev while Loeffler was still a small child. Later they lived in Hungary and Switzerland. Loeffler decided to become a violinist and studied in Berlin with Joachim, Kiel and Bargiel, then with Massart (and composition with Guiraud) in Paris. He played with the Pasdeloup Orchestra and in 1881 emigrated to the USA, where he shared the first desk with the concert master from 1882 to 1903. He appeared as a violinist–composer with the orchestra first in 1891 with the performance of Les Vieilles du Ukraine, and his works were performed regularly by the Boston Symphony (and by other American orchestra) for the rest of his life. Loeffler became a US citizen in 1887 and eventually resigned from the orchestra to devote himself to composition. He was a friend of Ysaÿe and John Singer Sargent, also of Fauré and Busoni (both of whom dedicated works to him), and later of George Gershwin.

Loeffler conceived a hatred of Germany after his father was arrested on spying charges. A man of wide culture and refined taste, he cultivated an idiom deeply imbued by contemporary French and Russian music, in the traditions of Franck, Chausson, Debussy. He often cultivated unusual combinations of instruments, and was one of the earliest modern enthusiasts for the viola d’amore, which he discovered in 1894 and wrote parts for in several scores. In his later years he also, unexpectedly, became deeply interested in jazz, and wrote some works for jazz band.