Mikhail Saakashvili, Georgia's president, has distanced the ex-Soviet republic from Russia and come closer to the European Union and Nato.
He says the Justice Party is financed by Moscow and is used as an instrument to undermine the government. Giorgadze's niece, Maya Topuria, received the longest prison term of 8 1/2 years.
Topuria's lawyer, Melinda Sarafa, said in a statement: "The verdict convicting Maia Topuria and her co-defendants is a lie, based entirely on false evidence.
"But this is not a surprise in a judical system that last year convicted nearly 17,000 of its people and acquitted less than 40."
At the start, the trial included 19 defendents arrested in September 2006, but six were acquitted in the course of hearings.
Russia denies any links to Giorgadze, although he often gives interviews to Russian television channels criticising Saakashvili, who is viewed with deep mistrust by the Kremlin.