The move is another blow to the troubled case.
Thamir al-Khuzaie was injured in the 8 November ambush in western Baghdad in which another defence lawyer, Adel al-Zubeidi, was killed.
Al-Zubeidi was the second defence lawyer involved in the case to be assassinated since the trial opened on October 19.
"I was only a lawyer who practiced his profession in Iraq. Yet I was subjected to an assassination attempt and to danger that might have even touched my family," al-Khuzaie said. "So I decided to leave the country."
He said that he had written to the ruler of Qatar asking for "humanitarian asylum" for him and his family.
Al-Khuzaie represented two of Saddam's seven co-defendants in the trial, which resumes on 28 November.Reuse content