Though we have no concrete details of Ohtar's life before his northward march with Isildur, we do have some clues. Most notably, we're told that he was Isildur's trusted squire and close in his lord's confidence, so he had presumably served with Isildur for some considerable time. Before its capture by Sauron, Isildur had held the tower of Minas Ithil on the borders of Mordor, and so it seems reasonable to assume that his faithful squire Ohtar would also have been stationed there.

Though Isildur failed to reach Arnor after the War, Ohtar was one of the very few survivors of the Disaster of the Gladden Fields to win through to the North-kingdom. We're not told where Ohtar eventually settled after delivering the Shards of Narsil. He might conceivably have made the long journey back to Gondor, but it seems more realistic to imagine that he would have remained in the Northern court of Valandil, his old master's son.