Only one out of 479 congress delegates voted against Medvedev's candidacy.
Medvedev was formally nominated December 10 by the United Russia party and minor pro-Kremlin parties as a presidential candidate. His nomination was later backed by President Vladimir Putin.
On December 11, Medvedev proposed that Putin be appointed prime minister after the March 2008 presidential election.
Before voting on Medvedev's candidacy, Putin said at the congress that he would agree to become Russia's prime minister if Medvedev wins the presidential election.
"If today Russians demonstrate their trust in Dmitry Medvedev, then I am ready to continue our common policy in the post of head of the Russian government," Putin said.
He also said he would work as premier without any reorganization of powers between the presidential and prime ministerial posts.
Medvedev, 42, a trained lawyer, worked under Putin in the early 1990s in the mayor's office of St. Petersburg, the president's hometown. In Moscow in 1999, he was appointed acting deputy chief of the presidential staff.
He also headed the president's campaign headquarters in the run-up to the 2000 elections. In 2003, he became chief of the presidential administration and retained the post until November 2005, when he was appointed first deputy prime minister and put in charge of an ambitious multi-billion dollar "national project" to improve living standards.