Oscar Emmanuel Peterson was born August 15, 1925, in the Little Burgundy neighborhood of Montreal, the son of West Indian immigrants: his mother Kathleen worked as a domestic, his father Daniel as a Canadian Pacific Railway porter who had taught himself organ, trumpet, and piano and became his first music teacher. Peterson began on trumpet and piano at five, but a bout of tuberculosis at seven sidelined his lungs and pushed him toward the keyboard exclusively. His sister Daisy gave him a classical grounding, and from age nine or so he studied with the Hungarian-born pianist Paul de Marky, himself a pupil of a Liszt student, drilling scales and études for hours a day. Hearing a recording of Art Tatum as a boy left a permanent mark; Peterson later said Tatum "scared me to death" and that he "was never cocky again." He dropped out of Montreal High School to work steadily, played in the Johnny Holmes Orchestra as a teenager, won a CBC national music competition in 1940 at fourteen, and built a local reputation on Montreal radio broadcasts through the mid-1940s.

Norman Granz heard one of those broadcasts by chance and brought Peterson to New York in 1949 for an unbilled, unrehearsed guest spot at a Jazz at the Philharmonic concert in Carnegie Hall; the ovation was immediate, and Granz became his manager and producer for most of the rest of his career. Peterson began working as a duo with bassist Ray Brown around 1950, then built a full trio around 1952 with Brown and a rotating guitar chair: Irving Ashby, then Barney Kessel, then, from 1953, Herb Ellis, whom Peterson later called the "most stimulating" of his early partners. That working trio was on tour in Japan in the fall of 1953 as part of a Jazz at the Philharmonic package when Peterson heard a young Tokyo pianist named Toshiko Akiyoshi and told Granz to record her; Granz did, cutting Toshiko's Piano (1954, Norgran) in Tokyo with Peterson's own touring rhythm section, Ray Brown on bass, Herb Ellis on guitar, and J.C. Heard on drums, behind her. It became her debut LP and the specific break that led to her scholarship at Berklee two years later; her career from that point on is covered in full in her JazzProfiles.com profile. Ellis left the trio in 1958 after On the Town with the Oscar Peterson Trio, recorded live at Toronto's Town Tavern; rather than replace him, Peterson brought in drummer Ed Thigpen, reasoning that no other guitarist could match what Ellis had done.

The Brown/Thigpen trio became Peterson's most heavily recorded unit. For Verve he cut an extended run of "Songbook" albums between 1959 and 1961 devoted to Duke Ellington, Cole Porter, George Gershwin, and other American songwriters (the Ellington volume, recorded in Chicago in the summer of 1959, is representative), alongside Very Tall (1961/62) with vibraphonist Milt Jackson and the trio's signature album Night Train (1963), which included Peterson's own "Hymn to Freedom," later adopted as an anthem during the civil rights era. In the early 1960s Peterson also co-founded and headed the Advanced School of Contemporary Music in Toronto with Brown and Thigpen, a short-lived jazz-education venture that closed after about five years for lack of funding. He composed Canadiana Suite, an eight-part tribute to the country he crossed repeatedly by rail, recorded September 9, 1964, and released the following year on Limelight; We Get Requests, cut at RCA's New York studios between October 19 and November 20, 1964, closed out a fourteen-year run with Verve. Brown and Thigpen both left in 1965, replaced by bassist Sam Jones and drummer Louis Hayes (later Bobby Durham).

Through the late 1960s and into the 1970s Peterson recorded extensively for the German MPS label at producer Hans Georg Brunner-Schwer's private studio in Villingen, releasing his first unaccompanied solo album, My Favorite Instrument (1968); Motions and Emotions (1969), an orchestral date with Claus Ogerman arrangements that took in Beatles material; and Tristeza on Piano (1970); much of this run was later compiled as the Exclusively for My Friends series. When Granz founded Pablo Records in 1973, Peterson followed him and rebuilt a piano-guitar-bass trio in the 1950s mold, this time with guitarist Joe Pass and bassist Niels-Henning Ørsted Pedersen; The Trio, recorded live at Chicago's London House in May 1973, won a Grammy for Best Jazz Performance by a Group. British drummer Martin Drew joined in 1974 to make it a working quartet that toured for years. The Pablo period was extraordinarily prolific: duo and small-group dates with Dizzy Gillespie (1974), Joe Pass (a duo Porgy and Bess, 1976), Count Basie ("Satch" and "Josh", recorded December 1974, and a 1977 sequel), Ella Fitzgerald and Ray Brown (Ella and Oscar, recorded May 1975), and live recordings from Montreux and elsewhere including Digital at Montreux (recorded July 1979) and Nigerian Marketplace (1981).

Peterson's honors accumulated steadily across these decades: DownBeat named him its readers'-poll pianist of the year for thirteen consecutive years beginning in 1950, and Canada made him an Officer of the Order of Canada in 1972 and a Companion in 1984. He continued performing and recording through the 1980s despite worsening arthritis and weight gain that limited his mobility, and chaired York University's jazz program in the early 1990s. A stroke in 1993 weakened his left side and kept him off the bandstand for two years; Prime Minister Jean Chrétien offered him the post of Lieutenant-Governor of Ontario, which Peterson declined because of his health. He returned to performing and recording for Telarc from the mid-1990s on, playing a style now led almost entirely by his right hand; friend and Ontario premier Bob Rae remarked that "a one-handed Oscar was better than just about anyone with two hands." Later albums included A Summer Night in Munich (1998) and Trail of Dreams: A Canadian Suite (1999-2000, with Michel Legrand), and he received a Grammy Lifetime Achievement Award in 1997. Peterson passed away of kidney failure at his home in Mississauga, Ontario, on December 23, 2007, at eighty-two.

Peterson's playing fused a classical virtuoso's technique, drilled into him as a boy by Paul de Marky, with a jazz vocabulary built on Art Tatum's example and, by his own account, on Teddy Wilson, Nat King Cole, and James P. Johnson before him. The result was a famously torrential, harmonically dense style, capable of stride-derived left-hand work, blues-drenched swing, and long, cascading right-hand runs, all delivered with a technical command that few pianists in jazz history have matched; Duke Ellington called him the "Maharaja of the keyboard," and guitarist Joe Pass said only Tatum and Peterson had achieved "total mastery" of their instrument. Some critics found the sheer density of notes a liability, arguing his playing could crowd out space and understatement in a way more minimalist pianists avoided; even admirers singled out his more restrained work, particularly as an accompanist behind singers like Ella Fitzgerald, as some of his most effective playing. His working format, a piano trio built around a guitarist rather than a horn, echoed Nat King Cole's earlier trio and, in its 1970s Joe Pass/Niels-Henning Ørsted Pedersen incarnation, became one of the most celebrated small groups in mainstream jazz. He was also a serious composer, most visibly on Canadiana Suite and the civil-rights-era standard "Hymn to Freedom."