Jacques Joseph Jean Diéval, known as Jack, was born on December 21, 1920, in Douai, in the Nord region of northern France. He became one of the best-known jazz pianists in postwar Paris, then a radio and television presenter, a composer of songs and library music, and a long-serving board member of the French authors' society SACEM. His parents were musicians who led a jazz ensemble called the Dédé Jazz Band. He studied at the Douai conservatoire with Victor Gallois and was playing professionally in Lille from the age of fourteen. Before the war he worked in northern France with the drummer André Jourdan, and during it he played in officers' clubs and toured Tunisia and Algeria; in 1942 he spent a short time at Tunis Radio.

In Paris he worked for the singer Lucienne Boyer and then, from 1943 to 1946, in the orchestra of Alix Combelle, where he stayed about two and a half years. German Wikipedia places him at a record session with Django Reinhardt and Hubert Rostaing in Paris on May 15, 1946. In 1947 he made records with the tenor saxophonist Don Byas and put his own quartet on 78s for the Blue Star and Le Chant du Monde labels. By 1948 he led a trio with the bassist Lucien Simoën and André Jourdan, and he accompanied Coleman Hawkins at the Théâtre Marigny. In 1949 he played the Paris jazz festival with the altoist Hubert Fol, directly after Miles Davis and Tadd Dameron, and the same year he became the regular accompanist of the singer Henri Salvador. The lyricist Boris Vian had already written two texts for him in 1945, "Ce n'est que l'ombre d'un nuage" and "J'ai donné rendez-vous au vent".

The Swing label recorded him steadily around 1949. He is the pianist on Hubert Rostaing's sextet 78 "Be-Bop Tune" / "Auber Blues", cut on December 30, 1948, and January 31, 1949, and he led a quartet that recorded "Tea for Two" with the trumpeter Bill Coleman on October 4, 1949, with Paul Vernon on tenor saxophone, Emmanuel Soudieux on bass and Richie Frost on drums. In Paris on February 10 and 22, 1950, he recorded a quartet and quintet session with the visiting tenor saxophonist James Moody, the trombonist Nat Peck, Soudieux and Frost, with Annie Ross singing on "Le Vent Vert"; the American label Prestige issued the sides as the 10-inch LP New Sounds From France. His own quintet, formed in 1953, included the trombonist Bill Tamper and the saxophonist Jean-Claude Fohrenbach.

In 1954 he created the radio programme Jazz aux Champs-Élysées for French radio and television, which he presented until 1972; it was renamed Musique aux Champs-Élysées in 1964. A house band, the J.A.C.E. All-Stars, played on it, and the first 10-inch LPs of the series, issued by La Voix de son Maître in 1954 and 1955, paired him with players such as the altoist Hubert Fol, the bassist Pierre Michelot, Fohrenbach and, on the second volume, the violinist Stéphane Grappelli. A 1957 Polydor LP under the programme's name carried the J.A.C.E. All-Stars, with the tenor saxophonist Guy Lafitte and the guitarist Sacha Distel among the players. He also produced and presented television programmes, among them Paris Carrefour du Monde and Club du piano, and he fronted the CBS compilation LP Jack Diéval présente: Club du piano n° 1 (1967). In the 1950s he led a trio with the trumpeter Doc Cheatham, accompanied Eartha Kitt and Gérard Badini, played the light-music festival in Stuttgart each year from 1954 to 1956, and was invited to a BBC festival in London in 1957. French Wikipedia credits his 1956 album Fou de rock'n'roll, by his Septuor, with the prize of the Disque-Jockey Association.

In 1961 he formed a trio with the bassist Jacques Hess and the drummer Franco Manzecchi, and guests who worked with it included Guy Lafitte, Lucky Thompson, Sonny Stitt, the singer Dionne Warwick and Eric Dolphy. On June 11, 1964, in a Paris studio, Diéval was the pianist in the septet that Dolphy led for a radio recording, with Donald Byrd, the tenor saxophonist Nathan Davis, Hess, the conga player Jacky Bambou and Manzecchi. It was made eighteen days before Dolphy's death and was later issued as Naima (1987) and Unrealized Tapes (1988), and in full in 2010. Later records of his own include the two-piano album Ambiance pour 2 pianos with Art Simmons, bassist Jimmy Woode and Manzecchi (Polydor, 1966), a quartet LP with the guitarist René Thomas (Relax, 1967), a Beatles EP with his trio (1967), and the 1969 Philips LP Le Chemin "Jazz Oratorio", in which his piano and the Paris Jazz Quartet, with Roger Guérin on trumpet, Michel Gaudry on bass and Jean-Louis Viale on drums, alternate modal jazz movements with the vocal soloist Maria d'Apparecida. In 1970 he played the Nice festival with Guérin, and in 1973 he composed Le Serpent Vert. A live double album from the Comédie des Champs-Élysées, 30 Years of Jazz From Gershwin to Duke Ellington (United Artists, 1976), has him leading a quartet with Guérin, the trumpeter Benny Bailey, Gaudry and Viale.

His best-known composition came in 1960: the melody of "J'ai le mal de toi", to words by Michel Rivgauche, which became known as "Parlez-moi de lui". Dalida recorded it in 1966, Françoise Hardy in 1968, and Cher in 1972 as "The Way of Love", with English words by Al Stillman. Alongside the jazz records he wrote and recorded a large body of light and library music for Chappell, including the Dance and Mood Music volumes with his orchestra. In June 1981 he went back to Douai for the filming of a documentary. SACEM elected him to its board in 1982, he became a vice-president in 1984, and he was re-elected in 1985, 1988, 1993, 1996 and 1997; in 2001 SACEM gave him its Grand Prix du jazz. He passed away in Paris on October 31, 2012, at the age of 91.

Diéval was nicknamed "le Debussy du jazz" and "l'impressionniste du jazz", names that suggest a light, colouristic touch on swing and bebop material. German Wikipedia reports that he named Earl Hines, Nat King Cole and Mel Powell as his influences, while Boris Vian heard a strong Teddy Wilson in his playing. He recorded straight-ahead small-group jazz in the 1940s and 1950s, a modal and operatic suite in 1969, and, for the library catalogues, short pieces for orchestra and for piano that move between jazz, waltz and easy listening. His reputation rests as much on his radio programme and his song as on his records, and the players around him on record included Bill Coleman, James Moody, Pierre Michelot and Franco Manzecchi.