Medvedev announced that the missile had traveled a record 11,547 km (7,170 miles), declaring it a serious part of the arsenal for some time to come.
"It seems to me that practically all tasks that were set, were successfully carried out," the president said, noting that data on the test would have to be analyzed.
An aide to the Russian navy commander said it was the first time a submarine had launched the Sineva ballistic missile to its maximum range.
"For the first time in Navy history, the launch was not to the Kura test range in Kamchatka [Russian Far East], but to the area of an equatorial part of the Pacific," Captain 1st rank Igor Dygalo said, adding that the launch was made to check the preparedness of naval strategic nuclear forces.
The Sineva launch was made as part of the Dvina tactical exercises of the Russian Northern Fleet, which are also part of larger-scale Stability-2008 exercises conducted with Belarus that started in September and will run until October 21.
Medvedev arrived Saturday along with Defense Minister Anatoly Serdyukov and Navy Commander Adm. Vladimir Kuznetsov to observe the exercises.
The Barents Sea portion of the drills involves more than 5,000 military personnel, eight surface ships and five submarines.
The exercises test Russia's strategic and regional deterrent and the structures of the Northern Fleet, particularly in relation to the naval strategic nuclear forces.
The RSM-54 Sineva (NATO designation SS-N-23 Skiff) is a third-generation liquid-propellant intercontinental ballistic missile that entered service with the Russian Navy in July 2007. It can carry four or 10 nuclear warheads, depending on the modification.
Russia's Strategic Missile Forces said last year that Russia would conduct at least 11 test launches of intercontinental ballistic missiles in 2008 and would double the number of launches after 2009 "to prevent the weakening of Russia's nuclear deterrent."