Moscow's relations with the West have plunged to a post-Soviet low over the annexation of Ukraine's Crimea peninsula and Russia's involvement in the conflict in eastern Ukraine.
Sarkozy met Russian President Vladimir Putin at his residence outside Moscow on Thursday after addressing the Moscow Institute of International Relations.
He told the institute it "does not make sense to isolate Russia" in the face of complex challenges like the crisis in Syria.
Russia has waged an aerial bombing campaign for nearly a month supporting the Syrian army, earning criticism from Washington, which accuses Moscow of targeting moderate opposition groups opposed to Assad's rule.
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"We must merge the two coalitions into one," Sarkozy said.
"Without Russia, one cannot meet the great challenges of this world," he said, adding that the global role of Putin is "more positive than negative, despite our differences."
After the speech Sarkozy, French president from 2007 to 2012, met Putin for informal talks, where they reminisced about past ties.
"The world needs Russia," he said, calling for mutual cooperation. "Russia and Europe are able to work together... To talk, listen and respect, that is the future for Russia and France," Sarkozy said.