A special Icelandic court found former prime minister Geir Haarde guilty on one count over the collapse of Iceland's banks in 2008.
But the court acquitted him of three other charges.
"Geir Haarde will not be punished," Markus Sigurbjornsson, the head of the never-before-used special court Landsdomur for current and ex-ministers, said.
Haarde, 61, was the first politician to be tried in connection with the global financial crisis.
He had rejected the charges against him. Today he was found guilty of not meeting with his cabinet when matters turned critical, the court said.
Haarde headed the right-leaning Independence Party and was prime minister from mid-2006 to early 2009 when his coalition was ousted amid public uproar over the crisis.
He was one of four former Icelandic government ministers blamed in a 2010 report for contributing to the country's stunning financial sector collapse in late 2008, when all its major banks, which at the time held assets equal to 923% of gross domestic product, failed in a matter of weeks.
The banking failure plunged Iceland into a deep recession, prompting a $2.1 billion bail-out from the International Monetary Fund, and sending the value of its krona spiralling. The country's economy has since returned to growth.
Parliament, now majority-held by Haarde's left-leaning opponents, voted in September 2010 that Haarde was the only one who should be tried for the collapse, including the online Icesave bank implosion that spawned a fiery diplomatic row with Britain and the Netherlands.
Last October, the court threw out the most serious charge of "gross neglect".
Haarde, whose trial opened March 5, has previously dismissed the case as a farce. He had risked up to two years in prison.
