The name Lochaber has two possible origins. The scholar William Watson favoured a Pictish or Welsh root, abar meaning river mouth, so Loch Abar would mean the confluence where the Lochy and Nevis rivers flow into Loch Linnhe. He conceded a second possibility: that abar comes from the Gaelic eabar, meaning mud or swampy place. Lochaber, in this reading, is simply the loch of swamps, named for a historic water feature on the Blar Mor, where the local high school and health centre now sit. Take your pick. The locals call themselves Abrach. Historically Lochaber stretched from the north shore of Loch Leven all the way past Spean Bridge to Roybridge, and at its widest included Glen Coe, Moidart, Ardgour, Morvern, Sunart, Ardnamurchan, and the Small Isles of Rum, Eigg, Muck and Canna. The main town is Fort William.

Lochaber appears first in Adomnan's seventh-century Life of Columba. Ardnamurchan Point is believed to have marked the boundary between Pictish lands to the north and the Irish-descended Dal Riatans to the south. Inverlochy Castle, the seat of the medieval lordship of Lochaber, was reportedly built on the site of an earlier Pictish settlement that the 16th-century historian Hector Boece described as a city much frequented by French and Spanish merchants before the Vikings destroyed it. Placenames suggest Viking settlement in Morvern and Ballachulish, but not further north or east. After Robert the Bruce won at Bannockburn in 1314, he gave Lochaber to his friend Angus Og MacDonald, Lord of the Isles. From Angus Og the territory passed through a sequence of MacDonald sons and grandsons, eventually being divided among the Camerons of Lochiel, the MacDonalds of Keppoch, the MacDonells of Glengarry, and other clans whose names still echo through these glens.

By the late 17th century, most of the Scottish Highlands were under tighter control: clan chiefs could be fined for crimes their followers committed. Lochaber was the great exception, identified by government officials, by other chiefs, and by Gaelic poets as a refuge for cattle raiders and thieves. Four clans were always named: the Glencoe and Keppoch MacDonalds, the MacGregors, and the Camerons. In September 1688, James VII outlawed the Keppoch MacDonalds after the Battle of Mulroy, shortly before he himself was deposed by the Glorious Revolution. From 1740, the Jesuit priest Father Alexander Cameron, a Clan Cameron nobleman, lived under a boulder at Brae of Craskie in Glen Cannich and ran an underground Catholic vicariate that covered Lochaber and Strathglass. Catholicism here was strictly illegal. Persecution had only made it tougher. From these glens came many of the men who answered Bonnie Prince Charlie's call in 1745.

After Culloden in April 1746, government troops moved through Lochaber on punitive raids, burning farms, driving cattle, and killing those they found. The Gaels still call that summer Bliadhna nan Creach, the Year of the Pillaging. What followed was worse: the Clearances of the early 19th century, when landlords replaced tenants with sheep, and the Highland Potato Famine of the 1840s. The poet Ailean a' Ridse MacDhomhnaill emigrated to Mabou, Nova Scotia, in 1816. Whole communities followed. After Laird Ranald George MacDonald's clearances at the height of the famine, the Highland and Island Emigration Society shipped Gaels from Lochaber and Moidart to the Colony of Victoria in Australia, where they founded Roman Catholic communities at Little River and Belmont. Their parish priest, Father Ronald Rankin, joined them in 1857. He is remembered today as the author of the Gaelic Christmas carol Taladh Chriosda. Lochaber emptied. The dialect survives in Glengarry County, Ontario, and in Cape Breton. The lordship of Lochaber, never formally abolished, simply faded. Since 1996 the Highland Council has had a Lochaber committee, which is now the only administrative trace.