Born in Chicago, Illinois, Ammons studied music with instructor Walter Dyett at DuSable High School. Ammons began to gain recognition while still at high school when in 1943, at the age of 18, he went on the road with trumpeter King Kolax's band. In 1944 he joined the band of Billy Eckstine (who bestowed on him the nickname "Jug" when straw hats ordered for the band did not fit), playing alongside Charlie Parker and later Dexter Gordon. Notable performances from this period include "Blowin' the Blues Away," featuring a saxophone duel between Ammons and Gordon. After 1947, when Eckstine became a solo performer, Ammons then led a group, including Miles Davis and Sonny Stitt, that performed at Chicago's Jumptown Club. In 1949 Ammons replaced Stan Getz as a member of Woody Herman's Second Herd, and then in 1950 formed a duet with Sonny Stitt.