Monk started playing the piano at the age of nine; although he had some formal training and eavesdropped on his sister's piano lessons, he was essentially self-taught.

In 1922 the family moved to Manhattan living at 243 West 63rd St., and Monk attended Stuyvesant High School, but did not graduate.

He briefly toured with an evangelist in his teens, playing the church organ, and in his late teens he began to find work playing jazz. He is believed to be the pianist featured on recordings Jerry Newman made around 1941 at Minton's Playhouse, the legendary Manhattan club where Monk was the house pianist. His style at the time is described as "hard-swinging," with the addition of runs in the style of Art Tatum. Monk's stated influences include Duke Ellington, James P. Johnson, and other early stride pianists.

Monk's unique piano style was largely perfected during his stint as the house pianist at Minton's in the early-to-mid 1940s, when he participated in the famous after-hours "cutting competitions" that featured most of the leading jazz soloists of the day. The Minton's scene was crucial in the formulation of the bebop genre and it brought Monk into close contact and collaboration with other leading exponents of bebop including Dizzy Gillespie, Charlie Christian, Charlie Parker, Miles Davis, Sonny Rollins, and Milt Jackson.