The judge, Midhat al-Mahmud, who heads the Supreme Judicial Council, was himself the target of an attack in December. He survived a suicide bombing of his home.
In the past two days, two senior Sunni clerics have also been killed in targeted attacks.
In separate violence today, a U.S. soldier was killed when a roadside bomb hit his vehicle south of Baghdad, and a police officer died in an explosion at his home near Hillah.
Overnight, one Iraqi soldier was killed when two army units clashed with each other.