Gus Viseur (born Gustave Joseph Viseur) was a Belgian-born accordionist who spent his working life in France and is the name most often given for the start of swing musette: Paris dance-hall accordion played with jazz phrasing over the rhythm guitar of the Ferret brothers. He was born on May 17, 1915 in Lessines, in the Belgian province of Hainaut, the son of a bargeman, and the family moved from place to place until it settled in Paris in 1920, so that he grew up in the city and his documented career, from the Paris fairs of the 1930s to his death in Le Havre, was spent in France. His father taught him the accordion from the age of eight and he later took lessons from a music professor. Father and son played in an amateur band from 1929, and after his father's death he worked the fairs and markets of Paris.

In the early 1930s he played second accordion for the bandleader Médard Ferrero. In 1933 he met the accordionist René "Charley" Bazin, and the two began to improvise after hearing jazz. He led a band of his own by 1935 that recorded four titles that year, and he had the reeds of his Fratelli Crosio accordion filed down and retuned so that the usual musette vibrato gave way to a plainer, more modern sound. He played in the orchestra of the pianist Boris Sarbek and worked in France and Belgium with the trumpeter Philippe Brun, Joseph Reinhardt and his own quintet. Discogs lists the 1939 Columbia single "Honeysuckle Rose" / "Whispering" (DF 2662) under his name with the Orchestre Victor under Sarbek's direction.

His jazz records begin with the Swing label that Charles Delaunay of the Hot Club de France had started. Discogs lists "It Had to Be You" / "Wind and Strings (Andalusia)" (Swing SW. 37, October 1938) under the name Gus Viseur's Music, with the guitarists Pierre "Baro" Ferret, Jean "Matlo" Ferret and René "Challain" Ferret and the bassists Maurice Speilleux and Antonio "Tony" Rovira; the Frémeaux compilation Compositions 1934-1942 gives September 28 and October 20, 1938 as the Swing recording dates of "Andalousie" and "Automne." From 1941 to 1943 he made further Swing singles with his own orchestra (SW. 106, 116, 125, 140 and 169), usually with the clarinettist André Lluis, a bassist and two of the Ferrets or Joseph Reinhardt on guitars. French Wikipedia says he was one of only two accordionists, with Charles Verstraete, to belong to the Hot Club de France. Georg Lankester's biography adds that he played with the saxophonist André Ekyan and Django Reinhardt in Paris clubs; no record credit with Reinhardt was found, but two of his Swing sides, "Swing 39" and "Swing 42," are Reinhardt compositions, and so is "Nuages," which he recorded for Columbia on September 23, 1942.

French Wikipedia lists him at the accordion on Édith Piaf's recording of "L'Accordéoniste," made in May 1940 with Wal-Berg's orchestra, and Discogs credits him there too, uncredited on the label; English Wikipedia says that session brought him wider public attention. His "Swing valse," written with Baro Ferret and recorded on August 9, 1940 with Matelo Ferret on guitar according to Discogs, became the best known of his compositions. In 1942 he and the trumpeter Gus Deloof made "Gus & Gus" / "Harlem Swing" for Decca, with Joseph Reinhardt and Roger Chaput on guitars, Jacques Lowens on clarinet and Jacques Petitsigne on bass. A 1952 Ducretet Thomson single of "Be-bop Polka" with the accordionist Loulou Legrand carries a Grand Prix du Disque note for 1952 on Discogs, which files it as a polka.

The long middle of his career was lighter music: the Pacific records of 1949 and 1955, the Barclay 10-inch LP Chansons de Paris (1955) and similar sets. Accounts of the 1960s differ. English Wikipedia reports a United States tour in 1963, after which he stopped playing and opened a record shop in Le Havre, while Lankester has the Le Havre shop opening in 1955 and a move to Canada in 1960, with a weekly television programme in Montreal. All accounts agree that he returned to the studio around 1970: a Vogue LP of 1969 (CLVLX. 327) and the Mode Serie LP Swing Accordéon (1971) followed, and on the second he plays "Swing 39," "Swing 42" and "Djangology" with Matelo and Pierre Ferret, the clarinettist Claude Civelli, the bassist Jacques Petitsigne and the drummer Roger Paraboschi. He passed away in Le Havre on August 25, 1974.

Viseur treated the accordion as a jazz solo instrument at a time when it belonged to the dance hall. Lankester counts him with Louis Richardet and Gorni Kramer among the first to play jazz on it, calls him a strong improviser and says his playing grew out of the Manouche style of Django Reinhardt and the records of Black American jazz musicians; Discogs files the Swing label singles as jazz and swing. Retuning the reeds to drop the musette vibrato gave him a drier, quicker tone that sits comfortably beside a clarinet and rhythm guitars. His reputation rests on the dance-hall accordion repertoire as much as on jazz, and the long run of waltzes, polkas and Paris songs from the 1950s onward is musette rather than improvised jazz; the jazz case is the Hot Club years of 1938 to 1943. The musicologie.org biography compares his importance for jazz accordion with that of Reinhardt and Stéphane Grappelli, and the accordionist Richard Galliano and the guitarist Sylvain Luc built their 2015 album La Vie en rose (Rencontres avec Édith Piaf et Gus Viseur) around the repertoires of Piaf and Viseur.