Fraser left Scotland sometime after 1745, possibly because of political troubles (the Frasers had supported the Stuarts, who were on the losing end of a rebellion). He set up trade on the upper Allegheny river, but was quickly run out of his cabin by the French. He moved further down the river - near modern-day Pittsburgh, built a new cabin and continued to trade.
Fraser was one of the settlers building a fort on the site of Fort Duquesne, (near his own land) when the French took over - again. Fraser supplied Washington's attempt to reclaim the fort in 1754 (which was followed by the defeat at Fort Necessity), and served as the Chief Scout during the Braddock Expedition.
After Braddock failed, Fraser gave up op the area - depriving the French of a third opportunity to chase him off his land, so I suppose that's a small victory. He moved to the Tuscarora valley, before finally settling at Fort Bedford.