Pachachi was born in Baghdad into the Abdah branch of the Shammar tribe. As the son of Muzahim al-Pachachi, nephew of Hamdi al-Pachachi and the cousin of Nadim al-Pachachi, he was the scion of a Sunni Arab nationalist family with a long tradition in Iraqi politics and a graduate from Victoria College, Alexandria in Egypt. He supported the 1941 Iraqi coup d'état led by Rashid Ali Al-Gaylani as a member of the Kata'ib al-Shabab (Youth Brigade).