State-controlled VTB, which bought into Rosbank in 2010, said in May that the stake was not a strategic investment and that it was in talks to sell the asset.
That followed upheaval at Rosbank when the bank's Chief Executive Vladimir Golubkov was charged with bribery. Golubkov was later dismissed from the bank.
Under the deal, VTB will sell the Rosbank stake to SocGen while the French bank will sell VTB shares it holds in Russian companies, loans to Russian companies and Russian real estate assets, the source said. The source did not disclose a monetary value for the deal.