Kadhimi said in a tweet that the security forces succeeded in arresting Ghazwan Alzawbaee, known as Abu Abida Baghdad, who was the "primary culprit” responsible for the bombing the killed 323 people on July 3, 2016 while crowds were shopping ahead of Eid al-Fitr.
Islamic State (ISIS) claimed responsibility for the attack.
"Holding those involved in the blood of our children accountable is a national duty that we will not deviate from,” he said.
The prime minister added that plans are in the works for a monument to commemorate the victims.
Reporter's code: 50101