The move Friday came three days after Defense Minister Anatoly Serdyukov was dismissed during a corruption investigation, RIA Novosti reported.
Serdyukov was replaced by Sergei Shoigu, who then nominated Gerasimov to be chief of the General Staff.
Gerasimov had been named commander of forces in the Central Military District in April.
The corruption charges against Serdyukov were seen as a pretext for getting rid of him, The New York Times reported. He had made deep cuts in the ranks of officers, alienating many in the military.
In approving Gerasimov, Putin told him he would have to calm tensions with defense manufacturers caused by frequent changes in orders.
Putin told the general he was counting on him to "establish stable, good collegial work" with military contractors.