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. He lived in London from about 1886 to 1892 where he was married with two children and divorced. After travels in Italy, France, Belgium, Switzerland, 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. Particularly in his pre-WWI piano music, he appears as an original Impressionist composer with a strong humoristic vein and programmatic ideas inspired by sounds in his environment including nature, traffic, and industry. One critic wrote, "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").
After the War, he developed his Celtic leanings. 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".
Hennessy wrote extensively for the piano, and also for many chamber music instrumentations, as well as a number of songs. Most of his chamber music dates from after World War I.
From the time Hennessy lived in Paris, his music was largely published by E. Demets and from 1923 by Max Eschig (who had taken over Demets). Other publishers included Augener (London) and Schott (Mainz).
For a full list of compositions, see List of compositions by Swan Hennessy. Dates below are years of publication.
Lieder an den Mond. Romantische Stücke, Op. 10, for violin, cello, piano (London: Augener & Co., 1888)
Sonate en style irlandais, Op. 14, for violin and piano (London: Schott & Co., 1904; as Sonate en Fa (style irlandais): Mainz: B. Schott’s Söhne, 1905)
Prémier Quatuor (Suite) [String Quartet No. 1], Op. 46 (Paris: E. Demets, 1913)
Deuxième Quatuor [String Quartet No. 2], Op. 49 (1920) (Paris: E. Demets, 1920)
Rapsodie celtique, Op. 50, for violin and piano (Paris: E. Demets, 1915)
Petit trio celtique, Op. 52, for violin, viola, cello (Paris: E. Demets, 1921)
Trio, Op. 54, for two clarinets and bassoon (Paris: E. Demets, 1921)
Variations sur un thème de six notes, Op. 58, for flute, violin, viola, cello (Paris: Max Eschig & Cie., 1924)
Quatre Pièces celtiques, Op. 59, for cor anglais, violin, viola, cello (Paris: Max Eschig & Cie., 1925)
Troisième Quatuor à cordes [String Quartet No. 3], Op. 61 (Paris: Max Eschig & Cie., 1926)
Sonatine celtique, Op. 62, for viola and piano (Paris: Max Eschig & Cie., 1924)
Rapsodie gaélique, Op. 63, for cello and piano (Paris: Max Eschig & Cie., 1925)
Deux Morceaux, Op. 68, for alto saxophone and piano (Paris: Max Eschig & Cie., 1926)
Trio, Op. 70, for flute, violin, bassoon (Paris: Max Eschig & Cie., 1926)
Quatre Morceaux, Op. 71, for alto saxophone or viola (Op. 71bis) and piano (Paris: Éditions Max Eschig, 1929)
Quatrième Quatuor à cordes [String Quartet No. 4], Op. 75 (Paris: Éditions Max Eschig, 1930)
Deuxième Sonatine, Op. 80, for violin and piano (Paris: Propriété de l'auteur, 1929)
Sonatine, Op. 81, for cello and piano (Paris: Propriété de l'auteur, 1929)
Variations sur un thème original dans le style irlandais, Op. 12 (London: Augener & Co. 1902; revised ed. as Variations on an Original Theme in the Irish Style, Augener & Co., 1903)
Au bord de la forêt, Op. 21 (Paris: E. Demets, n.d. [1907])
Étude, Op. 25 (Paris: E. Demets, 1907)
Nouvelles feuilles d'album, Op. 27 (Paris: E. Demets, 1908)
Variations sur un air irlandais ancien, Op. 28 (Mainz: B. Schott’s Söhne, 1908)
Croquis de femmes, Op. 33 (Paris: F. Durdilly, Ch. Hayet, successeur, 1911)
Petite suite sur les notes Mi Do Mi Fa Si Mi, Op. 34 (Mainz: B. Schott's Söhne, 1911)
Fêtes. Deux Morceaux descriptifs, Op. 36 (Mainz: B. Schott’s Söhne, 1911)
Valses caprices, Op. 41 (Paris: E. Demets, 1912)
Sonatine, Op. 43 (Paris: E. Demets, 1912)
Sentes et chemins (Nouvelles études d'après nature), Op. 44 (Paris: E. Demets, 1912)
Pièces celtiques, Op. 45 (Paris: E. Demets, 1912)
Croquis parisiens, Op. 47 (Paris: E. Demets, 1913)
Impressions humoristiques, Op. 48 (Paris: E. Demets, 1913)
Sonatine celtique, Op. 53 (London: Evans & Co. 1924)
Epigrammes d'un solitaire, Op. 55 (London: Evans & Co., 1924)
Trois Pièces exotiques, Op. 57 (Paris: E. Demets, 1922)
Étude de concert, Op. 60 (Paris: Max Eschig & Cie., 1924)
Rapsodie irlandaise, Op. 67 (Paris: Éditions Max Eschig, 1929)
Banlieues ... Six Petites pieces, Op. 69 (Paris: Max Eschig & Cie., 1929)
À la manière de ..., 5 volumes (Paris: Éditions Max Eschig, 1926–8)
Voice and piano
Lydia, Op. 23 (Charles Leconte de Lisle) (Paris: J. Hamelle, 1908)
Epiphanie, Op. 26 (José-Maria de Heredia) (Paris: J. Hamelle, 1908)
Deux Mélodies, Op. 30 (Joséphin Soulary, Charles Baudelaire) (Paris: J. Hamelle, 1908)
Trois Chansons écossaises, Op. 31 (Charles Leconte de Lisle) (Paris: J. Hamelle, 1907)
Trois Chansons espagnoles, Op. 42bis (Emmanuel von Geibel, Heinrich Heine) (Paris: E. Demets, 1921)
Trois Mélodies, Op. 56 (Charles Baudelaire, Albert Samain, Jean Ajalbert) (Paris: Éditions Max Eschig, 1925–32)
Trois Mélodies sur des poésies d'André Delacour et de Leconte de Lisle, Op. 66 (Paris: Max Eschig & Cie., 1926)
Trois Chansons celtiques, Op. 72 (Charles Leconte de Lisle, Anatole le Braz, Pierre Scize) (Paris: Éditions Max Eschig, 1927)
Deux Mélodies, Op. 73 (Paul Géraldy, Anatole le Braz) (Paris: Éditions Max Eschig, 1928)
Deux Mélodies, Op. 79 (Paul Verlaine, Prosper Blanchemain) (Paris: Éditions Max Eschig, 1934)
Quatre Pièces celtiques, Op. 59, in an arrangement for cor anglais and organ, performed by Manfred Hoth (cor anglais) and Ulrich Leykam (organ), on: K&M Records, CD [undated].
Trio, Op. 54 for two clarinets and bassoon, performed by Trio d'Ance di Bolzano, on: Rainbow RW 98107, CD (1999).
Quatre Pièces celtiques, Op. 59, in an arrangement for cor anglais and string orchestra, performed by Rachel Tolmie (cor anglais), Bourbaki Ensemble, on: Wirripang Wirr 018, CD (2008).
Trio, Op. 54 for two clarinets and bassoon, performed by Trio Pleyel, on: bremenradiohall records brh cd 1305, CD and downloads (2013).
