We have no specific dates for Gelmir before the Dagor Bragollach of I 455, but as one of the Noldor of Angrod's people, he almost certainly originated in the Blessed Realm, and followed his master into Beleriand as part of the Return of the Noldor.

Of his ultimate fate The Silmarillion tells us nothing, and indeed he is last mentioned in Nargothrond mere paragraphs before the Battle of Tumhalad and the Fall of that stronghold. On that basis alone, it would be conceivable that he remained in Nargothrond and was lost in the battle, or the sack that followed. The Children of Húrin, however, gives us rather more detail about Gelmir and his companion Arminas, making it explicit that they returned to Círdan before Nargothrond fell. Of Gelmir's fate after that point, we know nothing. He may have returned to Aman at the end of the First Age, or he may have remained with Círdan in Lindon for a time. Indeed, it is not entirely implausible that he was still to be found at the Grey Havens at the time of the War of the Ring, thousands of years after Nargothrond's fall.

The name Gelmir is not explained, and there are various possible sources for its elements. The most likely meaning is probably 'blue jewel', from ʒel 'sky blue' and mir 'jewel', though this interpretation is far from certain.