Siddig's parents met in the 1960s when his mother travelled to Sudan with a friend who introduced her to Siddig's father, a member of Sudan's ruling family at the time. Siddig's father was a student at Cambridge University in the 1950s and was proficient in English. Siddig's uncle Sadiq al-Mahdi was Prime Minister of Sudan from 19661967 and again from 19861989. Siddig is also the great-great-grandson of Muhammad Ahmad, a Nubian religious leader who was proclaimed the Mahdi by his disciples.