Swan Hennessy (24 November 1866 – 26 October 1929) was an Irish-American composer and pianist who lived much of his life in Paris.
Swan Hennessy was born in Rockford, Illinois, of Irish origin and grew up in Chicago. His father, Michael D. Hennessy (1837–1919), was a Cork-born former President of the Chicago City Railways. There is no proof for the assertion in Baker's Dictionary that he studied "general subjects" in Oxford, England, but he may briefly have attended one of the (private) public schools there, before pursuing musical studies in Germany at the Stuttgart Conservatory, in the mid-1880s. His teacher in composition was Percy Goetschius. After travels in Italy, France and Ireland, he settled in Paris from about 1903, where he died in 1929.
Although not from Brittany, Hennessy was a member of the short-lived Association des Compositeurs Breton before World War I and continued to mix with other members including Paul Le Flem, Paul Ladmirault, Maurice Duhamel, Louis Vuillemin, and others throughout the 1920s. He died from an embolic following a routine operation; the composer Georges Migot held the funeral speech.
Hennessy was married with Claire, née Przybyszewska (1883–1947); their son Patrice Hennessy (1910–1973) became a well-known literary man. They are buried in a family plot on Montparnasse Cemetery, Paris, division 28, section III.
Swan Hennessy wrote in an Impressionist style, often tending towards a late-romantic idiom. Many of his pieces with titles ending on terms like "celtique" or "irlandais" are inspired by Irish and Breton traditional folk melody, but he rarely quotes actual folktunes. As a member of the "Association des Compositeurs Bretons", he took part in many of their concerts. In a French obituary, he was called "le barde de l'Irlande" and is credited as having saved "l'ancienne mélodie celtique". He also incorporated humorous elements into his music: "Il fut un humoriste d'une verve drue dont la drôlerie était faite à la fois d'observation et d'invention, de fantaisie et de psychologie." ("He was a humourist of great verve whose humour derived from observation and invention, fantasy and psychology").