Louis Mazetier is a French pianist who has spent four decades playing the Harlem stride style of the 1920s and 1930s, and an online sheet-music publisher's biography counts him among the leading exponents of the style anywhere. He was born in Paris on February 17, 1960, and is living. He is also a practising radiologist, and for most of his career music has shared his working week with medicine.

French Wikipedia and German Wikipedia say he grew up in Aubusson, started classical piano lessons at seven and, at about fourteen, heard Fats Waller's records and began copying them by ear. In 1977 he went to Paris to study mathematics and then medicine, and the city's jazz cellars did the rest: he was playing in clubs from 1977 or 1978, among them Le Caveau de la Huchette. French Wikipedia says he began a piano duo with François Rilhac in 1983 and spent more than ten years with the washboard orchestra of Gilbert Leroux. The earliest record credit found is as second pianist, beside Rilhac, on two tracks of the Gilbert Leroux Washboard Group's Weary Blues (Djaz Diffusion, 1986). In 1988 he became the pianist of Paris Washboard, the Dixieland and swing group formed that year by the clarinetist Alain Marquet and the trombonist Daniel Barda. Its first record, When We're Smiling (Stomp Off, 1988), has him on piano with Marquet, Barda and Leroux, and he has stayed with the band through a long run of Stomp Off albums and tours of Europe, Australia and the United States.

His own records began in 1989 with Echoes of Carolina (Stomp Off), a two-piano album with Rilhac and a guest spot for Marquet. Drop Me Off in Harlem (Djaz Diffusion, 1991) was a solo program that includes Waller, James P. Johnson and Duke Ellington pieces. He then made two-piano records with the English stride pianist Neville Dickie, If Dreams Come True (recorded in London in May 1994, Stomp Off, 1995) and Harlem Strut (recorded at Kingston University in May 1995, Stomp Off, 1996). A run of piano records for the Swiss label Jazz Connaisseur followed: the solo albums Good Vibrations (recorded in the Alte Kirche in Boswil, Switzerland, on December 9, 1995, and issued in 1996) and In Concert - What a Treat! (1996), a piano and trumpet duo album with Peter Ecklund, A Friendly Chat (2001), Barrel of Keys (2002), a two-piano date with Dick Hyman recorded in Boswil on October 29, 2001, and the solo albums The Piano Starts Talking (2003) and Pianistically Yours (2007). The Arbors Records piano series then issued Tributes, Portraits and Other Stories (2008) and My Own Stuff (2011), volumes 18 and 24 of the series. He also made a duo album with the trumpeter Jean-Loup Longnon, Just Friends (2003).

From the 2010s he worked with the tenor saxophonist Michel Pastre: the trio album 7:33 to Bayonne (Jazz Aux Remparts, 2016) is billed to Pastre, Mazetier and Jérôme Etcheberry, and Fine Ideas (Camille Productions, 2023) is a trio with Pastre and the drummer Guillaume Nouaux. Scott Yanow's review of Fine Ideas in The Syncopated Times likened the group to an adventurous mid-1940s swing combo. Mazetier is also one of seven pianists on Nouaux's Guillaume Nouaux & the Stride Piano Kings (2020), alongside Rossano Sportiello and Bernd Lhotzky, and he plays piano on the singer Pauline Atlan's tribute Le Monde de Fats (Ahead, 2018), on which Pastre also appears.

French Wikipedia's list of laureates of the Académie du Jazz's Prix Sidney Bechet, the award for the best French traditional jazz musician, gives 1993 to Mazetier and Daniel Barda together. A 2016 profile of Paris Washboard in The Syncopated Times described him as the group's essential pianist, and reported that he works about 50 hours a week as a radiologist and still plays dates with the band. In a 2020 interview, Barda noted that the pianist Philippe Carment often substitutes when Mazetier's medical practice keeps him from touring.

Mazetier plays the piano style of the New York stride school, and his records are built from its repertoire: Fats Waller, James P. Johnson, Eubie Blake and Jelly Roll Morton, with Duke Ellington and Teddy Wilson as the swing-era bridge. English Wikipedia names the American stride pianist Donald Lambert as his greatest influence, with Blake, Johnson, Waller, Don Ewell, Johnny Guarnieri, Dick Wellstood and Art Tatum also listed. The sheet-music publisher's biography describes his playing as lively and very melodic and rooted in the earliest jazz pianists, with a modern ear taken from Tatum, Ellington and Wilson. Scott Yanow wrote that on Fine Ideas he also touches on boogie-woogie and bebop, and the tunes he wrote himself, such as "Big Filthy", "A Delicate Brute" and "The Ferocious Lamb" on My Own Stuff, add a personal voice to the tradition. AllMusic files him under stride, New Orleans jazz revival and early jazz.