Rahman is an ethnic Kurd from Halabja, the site of the 1988Halabja poison gas attack. He replaced Rizgar Mohammed Amin as chief judge on 23 January 2006. Amin had resigned after being criticised in the Iraqi media for appearing "too soft" on the defendants by allowing them to speak aloud in court without being recognized.
After Amin's resignation, Rahman headed the Supreme Iraqi Criminal Tribunal during the rest of the trial of Saddam Hussein for genocide, and when it sentenced him to death.
In December 2006, al-Rahman took his family to Britain on a travel visa, and three months later applied for asylum. He later cancelled his application.