Pirate attacks have been common off the Somali coast, and international navies have been deployed to counter them.
Somalia has been without a functioning central government since 1991, allowing the pirates to operate in the Gulf of Aden, one of the world's busiest shipping lanes.
The pirate who confirmed to Reuters that the MV Irene had been released on Monday was speaking from the coastal pirate stronghold of Eyl and gave his name as Hussein.
"We already left the vessel and now we are dividing our money," he said. "A helicopter brought the cash this morning."