Cesar Camargo Mariano was born in São Paulo on September 19, 1943. He never studied music formally and worked the piano out by ear from the age of thirteen. That same year, 1957, the American trombonist and arranger Melba Liston heard him and invited him to play at a jazz club in Rio de Janeiro; a Rio radio programme followed, billed as "The Boy Prodigy Who Plays Jazz." The pianist Johnny Alf became close to the family around the same time and eventually lived with them, and it was Alf who taught Mariano arranging and composition rather than any conservatory. São Paulo's TV Record put the teenager on air in a special called "Passport to Stardom."

He was a professional by his late teens, and in 1964 he formed the Sambalanço Trio in São Paulo with the bassist Humberto Clayber and the drummer Airto Moreira. The trio opened the João Sebastião Bar, one of the city's leading bossa nova rooms, and became its house group. It lasted barely two years and made four records: Sambalanço Trio (Audio Fidelity, 1964), a second self-titled album and Reencontro Com Sambalanço Trio (both Som Maior, 1965), and Lennie Dale E O Sambalanço Trio (Elenco, 1965) with the American dancer and singer Lennie Dale, which took Jornal do Brasil awards for best album and best show. The trio also backed the trombonist Raul de Souza on À Vontade Mesmo (RCA Victor, 1965), credited on the sleeve as the backing band with Mariano at the piano. In 1965 he cut a one-off big-band date, Octeto De César Camargo Mariano (Som Maior), whose two alternating rhythm sections put Clayber and Moreira on half the album and the bassist Sabá Oliveira da Paz, the drummer Toninho Pinheiro and the guitarist Heraldo do Monte on the other.

Sabá and Pinheiro became Som Três, the piano trio Mariano led from 1966 to 1971 while working as staff instrumentalist and arranger at TV Record. Its six albums, from Som/3 (Som Maior, 1966) through Som Três Show (Odeon, 1968), Som 3 (1969), Tobogã (1970), Um É Pouco, Dois É Bom, Êste Som Três É Demais (1970) and a final self-titled Odeon record in 1971, are the body of work his Discogs biography and the English Wikipedia article both describe as high points of Brazilian jazz. From 1967 the trio doubled as the band and arranging shop for the singer Wilson Simonal, whose Show Em Simonal Som Três shares billing on.

The 1970s made him famous for something else. He became musical director, arranger and producer for Elis Regina, whom he married and with whom he had two children, Pedro Mariano and Maria Rita, both later singers in their own right. He arranged all but one track of Elis & Tom, recorded at MGM Studios in Los Angeles between February 22 and March 9, 1974 and released that year on Philips, and played piano on three of its songs and electric piano on four more, sharing the keyboard chair with Antonio Carlos Jobim. He produced and mixed her albums from Elis (Philips, 1977), on which he also plays the entire keyboard section, piano, Fender Rhodes, Hammond organ and two synthesizers, through Transversal Do Tempo (1978), Essa Mulher (1979) and the boxed Saudade Do Brasil (1980), which he arranged, conducted and played as well as produced. The São Paulo critics' association gave him its best-arranger prize in 1972, 1974, 1978 and 1979. His own band of the period, Cesar Mariano & Cia., made São Paulo Brasil (RCA Victor, 1977), a keyboards-and-electric-guitar record cut on sixteen channels at RCA's São Paulo studio that has since become one of the most sought-after Brazilian jazz-funk albums of the decade, and a self-titled EMI follow-up in 1980.

Instrumental records took over from 1981, when he and the guitarist Hélio Delmiro recorded Samambaia for EMI, a duo album whose title tune became a standard of the Brazilian instrumental repertoire. A Todas As Amizades (1983) was cut in Los Angeles with Abraham Laboriel, Alex Acuña, Ernie Watts, Jerry Hey and Oscar Castro-Neves; Todas As Teclas (Barclay, 1983) paired him with the keyboardist Wagner Tiso; Voz E Suor (EMI, 1983) set him beside the singer Nana Caymmi. Prisma (Pointer, 1985), a two-piano record with Nelson Ayres, named the band he took onto the live Ponte Das Estrelas, recorded at Projeto SP in São Paulo on July 16, 17 and 18, 1986. A performance of the tune "Prisma" opened the CBS double album drawn from that year's Free Jazz Festival, the Rio and São Paulo festival that ran for sixteen editions from 1985, sharing the record with Wynton Marsalis, Gerry Mulligan, Egberto Gismonti, Ray Charles and Leny Andrade. Mitos (CBS, 1988) supplied the opening theme of the Globo telenovela Mandala, and CLIO awards for Chevrolet and Coca-Cola campaigns came from a parallel career writing advertising music.

He moved to the United States in April 1994 and has worked from there since, in duo and trio formats more than any other. He made three records with Leny Andrade: Nós (Velas), cut and mixed at Art-Mix Studio in São Paulo in December 1992 and issued in 1993; Ao Vivo, taped at the Teatro Guaíra in Curitiba and released in 2007, which won the Latin Grammy Award for Best MPB Album that year; and Momentos Da Bossa (2008), a United States issue of that material. Duo (Trama, 2002, and Sunnyside in the United States the same year) is a piano-and-guitar record with Romero Lubambo, by then a regular in Mariano's own quartet, and the two returned in 2005 with a three-disc Trama box shared with Pedro Mariano, on which Mike Stern and Dennis Chambers guest on one track. Piano & Voz, the father-and-son duo with Pedro, was nominated for Best MPB Album at the 5th Latin Grammy Awards in 2004. He also produced the Japanese alto saxophonist Sadao Watanabe's In Tempo (1994) and co-produced Viajando (1998) and Minha Saudade (2001).

The Latin Recording Academy gave him its Lifetime Achievement Award in 2006, the same year he was nominated for Producer of the Year. His memoir Solo, 464 pages published by Leya in 2011, was shortlisted for the 54th Prêmio Jabuti in the biography category. His most recent album, Joined (CLEF/PRA, 2017), issued as both a CD and a DVD, sets his São Paulo trio of Sidiel Vieira, Thiago Rabello and Conrado Goys against three European classical soloists he had met at the Música em Trancoso festival, among them the Berliner Philharmoniker clarinettist Walter Seyfarth and the violinist Rudiger Liebermann. It was nominated for Best Instrumental Album at the 18th Latin Grammy Awards in 2017, where he also appeared as a presenter.

Mariano's reputation in Brazil rests on two things that are usually named together: an unusually strong left hand and an unusually exact sense of swing, both audible on the Sambalanço Trio records of 1964 and both learned by ear rather than taught. Where the bossa nova pianists of the same rooms played sparely, he built the samba-jazz trio around a walking, chordal left hand that carried the groove instead of leaving it to the bass, which is why the Sambalanço and Som Três records read as jazz trios playing Brazilian material rather than as bossa nova with solos added. The arranger's ear is the other half of the sound: Johnny Alf taught him to write before he had any formal training, and he thinks in orchestration even at the keyboard, which is what makes the São Paulo critics' association giving him best arranger and best pianist in the same three years, 1982, 1983 and 1984, less of a coincidence than it looks. Reviewing Duo for All About Jazz in September 2003, Judith Schlesinger called two chordal instruments in a duo the hardest format to bring off and credited Mariano's "uncluttered approach" for why this one does, noting the rhythmic precision and the audible warmth between him and Romero Lubambo. His compositions have travelled further than his own records: "Samambaia," "Cristal," "Curumim" and "Don Quixote" are played by musicians who have never heard the originals.