Mining giant Rio Tinto has sold the scheme near Fort William to SIMEC and Liberty House, two members of international energy and metals group GFG Alliance.
The group said the £330 million sale, supported by the Scottish Government, included hydro plants at Lochaber and Kinlochleven as well as the Lochaber aluminium smelter and more than 100,000 acres of estate spanning the foothills of Ben Nevis.
Liberty House executive chairman Sanjeev Gupta said: "This transaction fits very well with our vision to develop a sustainable and competitive metals industry in the UK as a key part of our global industrial business.
"This is a natural next step for us in our Scottish investment programme and is a springboard for wider manufacturing growth, creating many more jobs in Scotland."
Scottish Rural Economy Secretary Fergus Ewing said: "The sale of both the smelter and hydro power station increases the chance of the site having a viable, long-term future.
"This is great news for the whole local community and especially for the workers at the smelter. Subject to all necessary agreed processes, the deal implemented will safeguard 150 jobs and has the potential to create hundreds more.
"With GFG Alliance, incorporating SIMEC and the Liberty House Group, as the successful bidder, I look forward to an exciting new chapter in the history of the Lochaber complex, with the UK's last remaining aluminium smelter at Fort William continuing as a key component of Scotland's industrial capability and a major source of employment in the Highlands and Islands."
The agreement follows Liberty's reopening of the mothballed steel plate mill at Dalzell in Motherwell.
Lochaber SNP MSP Kate Forbes said: "My hope was always to preserve jobs and continue operations at the smelter, but I think that Liberty House's ambitions for the smelter could put Fort William in the driving seat of industrial expansion, career opportunities and sustainable economic growth.
"Innovation and community benefits were the foundation stones on which the smelter and the hydro scheme were first founded - new villages were built and electricity was generated in Lochaber before anywhere else in Scotland.
"I know that the Scottish Government and I were always keen to support a buyer who were committed to the local community.
"I think that Liberty House's plans for the region are reminiscent of the smelter's innovative, community-focused origins."