Cameron announced the Arctic Convoy Star during question time Wednesday, Sky News reported. About 400 of the thousands of sailors who guided merchant vessels to Murmansk and Arkhangelsk are believed to be alive.
At least 3,000 sailors died on what Prime Minister Winston Churchill described as "the worst journey in the world."
The sailors were not recognized after the war because the Soviet Union, an ally against Nazi Germany, quickly became an enemy.
A campaign to honor the Arctic Convoy veterans began soon after the fall of the Soviet Union.
Commander Eddie Grenfell, 92, of Portsmouth survived the sinking of a ship on the route. He told Sky News he was "pleased but not delighted" to hear of the medal because of the time it took.
"In the meantime, God knows how many of my Arctic Convoy chums have died waiting," he said.
Cameron said air crew on the Murmansk Run should get a Bomber Command clasp.
Veterans are likely to have to wait months more while the Ministry of Defense works out the details.