There have been months of intense speculation on whom Putin saw as his likely successor in the March 2 voting, along with the wider question of what Putin himself will do once he steps down.
Putin's popularity and steely control is so strong that most observers expect that whomever he supports would be a shoo-in.
Putin had long been seen as trying to choose between Medvedev, a business-friendly lawyer and board chairman of state natural gas giant Gazprom, and Sergei Ivanov, another first deputy premier who built up a stern and hawkish reputation while defense minister.
Although Putin is banned by the constitution from seeking a third consecutive term in office, he has indicated a strong desire to remain a significant power figure. He has raised the prospect of becoming prime minister, and his supporters have called for him to become a "national leader" with unspecified authority.