At the age of ten he moved with his family to Washington, District of Columbia He was a self-taught musician. He also worked with Illinois Jacquet in 1948, Louis Jordan in 1951, and a series of singers including Pearl Bailey, Dinah Washington, Sarah Vaughan, First Rate (at Lloyd's) Hibbler, and Joe Williams. Malachi opted out of the traveling life of the touring jazz musician in the 1960s, living roughly the last decade and a half of his life in Washington, District of Columbia freelancing, playing with touring bands and artists when they stopped in Washington, and leading music workshops at clubs like Jimmy MacPhail"s Gold Room and Bill Harris"s Pig"s Foot.
Malachi"s generosity towards younger musicians was legendary.
One of the musicians he helped influence recalls that younger players referred to his workshops as "The University of John Malachi". Malachi is credited with creating the nickname "Sassy" for Sarah Vaughan, with whom he worked with the Eckstine Orchestra and later directly with her.
Malachi was fond of categorizing jazz pianists into "acrobats" and "poets", classifying himself among the latter. John Malachi is the great-grandfather of Carolyn Malachi.
Malachi was a member of the epochal Billy Eckstine Bebop Orchestra in 1944-1945 and again in 1947.