"They released me, I think they let me out on the highway to Basra," the reporter, Carlos Raleiras, told his radio station TSF from Iraq by mobile phone.
The reporter said he had been taken in the boot of a car by his captors to the location in the southern Iraqi desert a few kilometres (miles) from the Kuwaiti border where he was released.
Raleiras added he had not been mistreated during his captivity.
He had been moved from house to house during his captivity and had been given water and crackers to eat by a group of up to nine captors.
Gunmen took Raleiras captive on Friday after they ambushed a three-jeep convoy of nine Portuguese journalists who were travelling to the southern Iraqi port city of Basra to cover the arrival there of 128 Portuguese military police.
The gunmen had reportedly demanded 50,000 dollars (42,550 euros) for the release of the journalist.