Tosh was born in Westmoreland, the westernmost parish of Jamaica. He was abandoned by his parents and “shuffled among relatives”. When McIntosh was fifteen, his aunt died and he moved to Trenchtown in Kingston, Jamaica. He first learned guitar after watching a man in the country play a song that captivated him. He watched the man play the same song for half a day, memorizing everything his fingers were doing. He then picked up the guitar and played the song back to the man.

The man then asked McIntosh who had taught him to play; McIntosh told him that he had. During the early 1960s, as an aspiring musician, Tosh went to vocal teacher Joe Higgs, who gave free music lessons to young people. Through his contact with Higgs, Tosh met Robert Nesta Marley (Bob Marley) and Neville O’Reilly Livingston (Bunny Wailer). He then changed his name to Peter Tosh and the trio started singing together in 1962. Higgs taught the trio to harmonize and while developing their music, they would often play on the street corners of Trenchtown.