The ICC said the two may be released to a state willing to accept them under as yet unknown conditions.
In 2011, Gbagbo refused to hand over power to President Alassane Ouattara, sparking violent protests in the country. French troops and the United Nations intervened to stop the fighting and found Gbagbo hiding in a bunker with his wife.
Thousands died and hundreds of thousands were displaced during the ensuing civil war.
Judges of the international court ruled Gbagbo and youth minister Blé Goudé had no plans to retake power after the vote, so there was "no need for defense to submit further defense, as the prosecutor has not satisfied the burden of proof."
The ICC has been accused of being one-sided in aftermath of the 2011 protests, with prosecutors focusing on Gbagbo and his regime rather than Ouattara commanders.
Gbagbo came to power in 2000 and managed to hold off another election for a decade. The 2010 vote forced a runoff the next year, which Ouattara won.
Nicholas Sakelaris contributed to this report.