Gelmir was originally of Angrod's people that ruled Dorthonion before the Dagor Bragollach. When Dorthonion was overrun during that battle, he fled south with a number of survivors to the safe havens of Círdan. Sometime between FA 490 and FA 495, he and his companion Arminas traveled to Nargothrond warning Lord Orodreth of the impending threat to the realm. He and Arminas's counsels were dismissed by Túrin, the High Captain of Nargothrond whom Orodreth ultimately deferred to in matters of war. Gelmir and Arminas eventually departed south and reported what they were told to Círdan.
His fate is unknown.