The court ordered Gelman to pay Yakemenko damages in the amount of 100,000 rubles ($29,000).
Yakemenko's complaint was connected to claims made by Gelman in messages on Twitter and LiveJournal in November 2010 that the youth agency head ordered the attack.
Several media outlets reported previously that Gelman thought activists from youth organization Nashi, created by Yakemenko, carried out the attack.
Yakemenko spokeswoman Kristina Potupchik said on Twitter that Yakemenko will give the money to the Nework of Putin's Supporters to hand out flowers across the city on March 1.
Kashin was attacked at night in November 2010 in front of his building by unknown assailants. He sustained serious injuries and was in a coma for a week. Neither the assailants nor the person who ordered the attack have been found.
Kashin himself was sued by Yakemenko for theorizing that the Nashi founder had been behind the attack but was cleared by a Moscow court in June. Yakemenko took issue with the journalist's statement, "I do not doubt the 'Yakemenko' version, and I have no other versions."