Said to have been a piano prodigy, Mittoo began his career in his mid-teens in Kingston, Jamaica. He worked in turn with the Rivals, Sheiks, and Skatalites and was a major figure (keyboard player, composer, arranger, producer) at Coxsone Dodd's Jamaican Record Manufacturing Co (familiarly, Studio One), where he led, or was a member of, a succession of studio groups (Soul Vendors, Sound Dimension, Invaders, Brentford All Stars, New Establishment) and backed Bob Marley and The Wailers, Jimmy Cliff, the Heptones, Delroy Wilson, Alton Ellis, and others.
Several of Mittoo's songs and/or rhythms from the 1960s were later recorded or adapted by other artists - eg, 'Real Rock' by The Clash and Willie Williams (as 'Armagideon Time'), 'Full Up' by the Mighty Diamonds (as 'Pass the Kouchie') and Musical Youth (as 'Pass the Dutchie') and 'Feel Like Jumping' by William Orbit. His own recording of 'Ram Jam' was a hit and led in 1967 to a tour of England with the Soul Vendors. Mittoo also played on the US soul singer Johnny Nash's Jamaican recordings of 'Hold Me Tight' (1968) and 'Cupid' (1969), which were among the first reggae songs to enjoy broad popularity in North America and Europe.
Mittoo moved in 1969 to Toronto, but continued to work in Jamaica and toured, and/or recorded, as a member of the Skatalites and with Byron Lee and the Dragonaires, Sugar Minott, Johnny Osbourne, Willie Williams, and others. He was music director in 1980 for a short-lived Broadway production, Reggae, and further supported reggae's growing acceptance in mainstream pop through the guidance he offered non-Jamaican bands like England's UB40, with which he recorded (Labour of Love, Virgin DEPCD-5) and toured in 1983.
In Toronto, Mittoo performed in local lounges and during the 1970s recorded LPs of instrumental reggae for Summus (Wishbone, SUS-50002) and the CTL (Reggae Magic, CTLS-5164/Pickwick PC-44015; Let's Put It All Together, CTLS-5189/U Artists UA-LA-442). There, as elsewhere, he assisted local reggae bands and artists, including Earth, Roots and Water, Esso Jaxxon (R. Zee Jackson), Carl Harvey, Lord Tanamo, Boyo Hammond, Carl Otway, the Sattalites, and Jackie James. He was inducted into the Black Music Association of Canada Hall of Fame in 1985.
Mittoo's discography also includes LPs issued by Coxsone (In London, CSL-8009; Evening Time, CSL-8012; Keep on Dancing, CSL-8020), Studio One (Showcase, SOL-0130; Macka Fat, SOL-1120; Now, SOL-9016), Third World (The Keyboard King, TWS-501; Hot Blood, TWS-912; In Cold Blood, TWS-931), and Wackie's (Wild Jockey, W-2749). All were distributed in Canada by his own company, Jackie. Many of the ska, 'blue beat,' 'rock steady,' and reggae recordings in which he participated at Studio One have been included in several CD reissues by Heartbeat - eg, Full Up: Best of Studio One, Vol 2 (HB-14), Downbeat the Ruler (HB-38), and Fire Down Below (HB-81).