Originally from Yibna, he was forced to leave his home Village in 1948 when he settled with his family in Rafah Refugee camp. He worked as a teacher until 1954 when he went to Egypt to study law in Cairo University. He was qualified from Egypt as a Lawyer involvement in the late 1950s. When the Fatah organization formed in the late 1950s, Youssef was an early activist, traveling to Qatar to form similar groups, and taking command of Fatah's military wing.
In 1968, Youssef was appointed to the Executive Committee of the Palestine Liberation Organization. He also was a member of the Palestinian National Congress, the Palestinian parliament in exile. Before his death, Youssef was interviewed by the Beirut newspaper L'Orient-Le Jour . In the interview, he explained his conviction to the Palestinian cause: "We plant the seeds, and the others will reap the harvest... Most probably we'll all die, killed because we are confronting a fierce enemy. But the youth will replace us." 
Youssef was alleged to have been linked to the 1972 Munich massacre, in which 11 Israeli athletes and coaches were killed in the crossfire between the German police and the Black September group. This prompted Israel to launch a revenge campaign called Operation Wrath of God, with Youssef as a principal target. In 1973, Israel sent commandos to Beirut, Lebanon to kill a number of high level PLO officials in the 1973 Israeli raid on Lebanon. Youssef and his wife were killed by gunfire in their bedroom when troops stormed into their Beirut apartment.