Nabil Hussein, 30, was beaten and then arrested and held at Mosul police headquarters. His father, Noureddine, 59, was detained when he went to the police station to inquire about his son.
"They put us in very small rooms. There was very little food and water," said Hussein. "We were insulted and humiliated by the Iraqi police the whole time."
Reuters Global Managing Editor David Schlesinger welcomed the release but called for an investigation into the incident.
"I am very pleased at the release, but I believe it is vital for the safety of all journalists working in Iraq that the circumstances of his detention be investigated thoroughly," he said.
Hussein, who is also a producer, has worked as a stringer for the London-based international news agency since 2003.