Attell was born on July 18, 1885 to a struggling Jewish family that, by one account, eventually had eighteen children. As a poor Jewish kid of diminutive stature raised in a tough Irish neighborhood, Attell began his career as a fighter from a very early age. As his older brother Abe Attell (1884–1970) was the Featherweight Champion of the World during the same period, Monte and Abe became the first brothers to simultaneously hold world boxing titles. Their brother, Caesar, also fought and was called "Two and a Half," for always giving that amount whenever the hat was passed for charity at boxing events. Like his brother Abe, Monte spent some of his youth and likely some of his later life selling newspapers for a living. At the age of 14, Attell was treated for burns to the face and hands from a childhood accident with a toy cannon which may have contributed to his decline as a boxer as he aged.