Man nicknamed ‘Merchant of Death’ tells court in Thailand that he has been framed.
It will take effect from the next presidential election in 2012 and also extends State Duma – the lower house – terms from four to five years.
Once Medvedev has signed the reform it will become law.
Critics have voiced concern that the move is being planned in advance of Vladimir Putin, the prime minister, returning to his former post as president.
However, this has been denied by officials.