Radayev, 52, a former head of the Saratov regional assembly, had been serving as acting governor since last month, when his predecessor Pavel Ipatov left office.
Experts said Radayev's nomination by President Dmitry Medvedev was the culmination of a power struggle waged by Volodin, a former senior United Russia heavyweight who serves as the deputy head of the presidential administration.
Volodin, a Saratov native and a rival of Ipatov, had pushed to install his trusted lieutenant Radayev in the post.
Also on Thursday, the Moscow region legislature voted by an overwhelming margin to make Emergency Situations Minister Sergei Shoigu the region's head.
Shoigu is the most popular minister in the Cabinet, with a 70 percent approval rating, according to a survey by state-run pollster VTsIOM last year.
