Jean-Loup Longnon was born in Paris on February 2, 1953, into a family of writers and musicians, and is a trumpeter, pianist, singer, composer, arranger and bandleader. English Wikipedia describes him as the nephew of the trumpeter Guy Longnon. He studied piano and cello first, and at fifteen turned to jazz and taught himself the trumpet, learning from records of Dizzy Gillespie among others. He is living, and his most recent album appeared in 2025.

According to English Wikipedia he started out in groups called the Jazzerinos and the Dixie Cats, and soon afterwards played with the organist Milt Buckner, the saxophonist Chris Woods, the organist Rhoda Scott and Jef Gilson. The earliest recording credit found is a bugle solo on "Havona" on Laurent Cokelaere's Coke Tales (Caravage, 1983). His own first album was a big band date, Torride!, recorded on July 13 and 14, 1984 for the 52e Rue Est label: he plays trumpet, bugle, piano and synthesizer, wrote all of the music, and is joined by the saxophonist André Villeger, the trombonist Denis Leloup and the drummer Umberto Pagnini, among others. Discogs files it under big band and jazz-funk, and its first side is a suite called "Suite Aquarelle".

On January 19, 1985 he was the trumpeter in a quintet with Michel Legrand, Leloup, the bassist Marc Michel and the drummer François Laizeau at Fat Tuesday's in New York, a set later issued on Verve as Live at Fat Tuesday's (1990). His own website says that while he was living in Manhattan he recorded some of his big band pieces there, with several members of the Vanguard Orchestra and the saxophonist Ted Nash as co-leader. Jean-Loup Longnon & His New York Orchestra was recorded on June 22 and 23, 1987 and issued by Atlantic in 1988, with Walt Weiskopf and Ralph Lalama on tenor saxophone, Michael Philip Mossman among the trumpets, Ed Neumeister on trombone, Gary Dial on piano and John Riley on drums. It mixes his own pieces ("Vous allez jouer du bop", "Nathalie...Un Matin" and "Torride", on which he also sings) with "Moment's Notice", "Body and Soul" and "Royal Garden Blues".

His writing also runs to the concert hall. Brass Création (Arion, issued in 1987) holds his symphonic poem L'Ours for brass quintet and orchestra, beside works by Patrice Caratini and Martial Solal, and he wrote its liner notes; his own site says the score has no reference to jazz and draws on the French school and on Hungarian, Russian and Austrian composers of the early twentieth century. Cyclades (JMS, distributed by Sony) is a suite of original pieces named for the Greek archipelago that joins a jazz orchestra of variable size with a symphony orchestra, and ends with his arrangement of "La Marseillaise". In Paris on November 11 to 13, 1991 he was the trumpeter on "Blues March", the closing track of Benny Golson's Domingo (Dreyfus Jazz), with Curtis Fuller, Kevin Hays and James Genus.

Bop Dreamer (Pygmalion Records, 1998) documents a septet he led at the Marciac festival on August 12 to 14, 1996, with the trumpeter Flavio Boltro, the tenor saxophonists Lionel Belmondo and Yannick Rieu, the pianist Pierre de Bethmann, the bassist Christophe Wallemme and the drummer François Laudet; two of its tracks add the Anna Gramm Delirium Big Band. The Académie du Jazz gave him its Prix Django-Reinhardt in 1991 and the Django d'or for best French jazz musician in 1995, and French Wikipedia also lists a Prix audiovisuel de l'Europe in 1984 and a second Django d'or in 2010, in the SACEM creation category. In 2003 he recorded the duo album Just Friends with the stride pianist Louis Mazetier, bop and stride face to face, with Longnon on trumpet and scat vocals.

In 2008 he re-formed his big band around younger players. Its live concert in Paris on May 29, 2008 became Encore du bop ???, and his site quotes praise for the band from the French press, including Le Monde. His quintet, which his site lists with the tenor saxophonist Antoine Daures, the pianist Ludovic Allainmat, the bassist Fabien Marcoz and the drummer Frédéric Delestré, recorded Just in Time (2015), and he has also led a Franco-Russian quintet with musicians from Saint Petersburg. A Jerusalem Post notice of February 27, 2014 announced five concerts in Israel. On June 18, 2014 he conducted the Paris-Calvi All Stars Orchestra in the opening tribute of the Calvi Jazz Festival to its founder René Caumer, who had passed away in August 2013, and the concert was recorded for the album R comme René (2015). His most recent album, Istanbounce (Continuo Jazz, June 6, 2025), is a full orchestra record for which he arranged all of the repertoire and wrote most of the originals, with Chloé Cailleton among the singers, and in April 2026 Couleurs Jazz published a questionnaire interview with him.

Longnon is a bebop trumpeter who writes for large forces. His own site presents his quintet as a small big band built on bop roots, and Discogs tags Torride! as big band and jazz-funk and Encore du bop ??? and Just in Time as bop. He names Ravel, Debussy, Dutilleux, Fauré, Poulenc, Stravinsky and Bartók among the twentieth-century composers he is steeped in, and he has written several scores for symphony orchestra; hence the Orchestral Jazz tag, applied to Cyclades and L'Ours rather than to his usual output. In his own list of favorite jazz musicians he names Thad Jones, Gillespie, Clark Terry and Art Tatum, and his site carries endorsements from Gillespie and Terry, the latter calling him a trumpeter of fantastic facility. A line quoted on his site says his big band sounds as if Thad Jones and Ravel were dining together at the devil's table.