Schroeder's intention of joining the Rosneft board had drawn criticism from his successor as chancellor, Angela Merkel, and from Martin Schulz, the leader of Schroeder's center-left Social Democrats in Germany.
But Rosneft CEO Igor Sechin, a close ally of Russian President Vladimir Putin, said Schroeder's arrival will "allow the development of the company's European business and the expansion of its European footprint."
The Interfax news agency cited Schroeder as saying he saw his role as Rosneft chairman as a broker of compromises when opinions differ on the board. Schroeder has previously said he wants to increase the energy security of Germany and Europe.
Schroeder is already the head of the shareholders' committee for Nord Stream, a pipeline transporting gas from Russia to Germany that is majority-owned by the Russian state gas company Gazprom.
Rosneft is majority-owned by the Russian government, with stakes also held by BP, Swiss commodities firm Glencore and Qatar's sovereign wealth fund.
Glencore and the Qatari fund are in the process of selling most of their stakes to CEFC China Energy Company Limited.
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