Pritchard, whose father was a violinist in the London Symphony Orchestra, studied violin, piano, and conducting in Italy. After ill health forced him to curtail his military service in World War II (1943), he became conductor of the Derby String Orchestra. In 1947 he joined the Glyndebourne Festival Opera, where he made his conducting debut in the second half of Don Giovanni (1949); he later served (1969–77) as musical director at Glyndebourne, which he used as a base for his extensive travels.

In 1952 Pritchard made his debut at the Royal Opera House, Covent Garden, where he conducted the premieres of Benjamin Britten's Gloriana (1953) and Sir Michael Tippett's Midsummer Marriage (1955) and King Priam (1962). As the musical director of the Royal Liverpool Philharmonic (1957–63), he introduced Britain to the “Musica Viva” concept, in which the performance is preceded by a spoken introduction and musical samples. He was music director of the London Philharmonic (1962–66), touring with them in the Far East (1969) and China (1973). He was chief conductor of the Cologne Opera (1978–89) and the BBC Symphony Orchestra (1979–89), as well as music director of the Belgian Opera Nationale (from 1981) and the San Francisco Opera (from 1986). He was knighted in 1983.