Belfast shipyard Harland and Wolff has been bought by InfraStrata, a UK based energy company.
The new owners are focused on the development and commercialisation of advanced high-value energy infrastructure projects across the world.
The shipyard entered administration in August under business advisers BDO, following the collapse of its Norwegian parent company.
InfraStrata, which is believed to be paying some £6million for the Belfast operation, plans to increase the workforce by several hundred over the next few years.
Around 120 jobs were put at risk and the future of a yard, which built the Titanic, was plunged into uncertainty.
All workers at the plant who did not take voluntary redundancy when the yard went into administration - 79 in total - will now keep their jobs.
Infrastrata chief executive John Wood said: "Harland and Wolff is a landmark asset and its reputation as one of the finest multipurpose fabrication facilities in Europe is testament to its highly skilled team in Belfast."
Welcoming the announcement Unite regional secretary Jackie Pollock said: "While politicians on all sides threw up their hands, claiming that the shipyard could not be saved and efforts should be focused on securing redundancy payments, the workers stepped up and took control.
“This is one of the most significant victories won by trade unions in Northern Ireland, and it is due to the efforts of the workers themselves supported by their unions and officials.
“Today’s lesson is clear: when working people organise, everyone wins!”, Mr Pollock said.
Workers have occupied the site since the business went into administration in the summer, undertaking a high-profile campaign to save their jobs.
The shipyard, whose famous yellow cranes Samson and Goliath dominate the east Belfast skyline, employed more than 30,000 people during the city's industrial heyday but the workforce numbered only around 125 when the company went under.
The business had diversified away from shipbuilding in the last two decades, shifting to work on wind energy and marine engineering projects.
Known around the world for building the doomed White Star liner Titanic, which sank on her maiden transatlantic voyage in 1912 after striking an iceberg, Harland and Wolff was one of the UK's key industrial producers during the Second World War, supplying almost 150 warships.
Northern Ireland Secretary Julian Smith welcomed the deal.
"I am delighted by the news that InfraStrata have purchased the Harland and Wolff shipyard and retained the skills and experience of the existing workforce," he said.
"I firmly believe that the shipyard has a promising future and that InfraStrata's plans present an exciting opportunity for both Belfast and Northern Ireland's manufacturing and energy sectors."
The Ulster Unionist Party’s East Belfast MLA, Andy Allen MBE, has welcomed the news that InfraStrata has bought the Harland & Wolff Shipyard and saved almost 80 jobs, as a vindication for the workforce who fought so hard against the closure of the yard.
UUP MLA for East Belfast Andy Allen said it's great news for east Belfast and 'Northern Ireland plc'.
"It is a vindication for the workers who were determined that this iconic site with all its industrial history and heritage would not be allowed to simply disappear without a fight. This is a victory for the workforce and the trade unions and a testament to their resilience.
"InfraStrata have exciting plans for the site and hope to create several hundred new jobs in the next five years which is great news in the current economic climate.
"We will do all we can to support the Shipyard going forward and help it to flourish,#" he said.
Trade unions Unite and GMB hailed the workforce's role in securing the yard's future.
Susan Fitzgerald, regional co-ordinating officer with Unite, said: "From July 29th, when workers were faced with the imminent collapse of the yard, they were determined not only to save their own jobs but to safeguard Northern Ireland's skillbase going forward. Their nine-week occupation will be remembered by future generations of workers as evidence of the power of collective action."
Denise Walker, senior organiser with GMB, said workers "took control of the situation and of their workplace".
"In so doing they have ensured that Harland and Wolff will not only continue but will be in a position to expand and fulfil its potential as a lynchpin of Northern Ireland's economy," she said.
Workers are now set to be involved in works on InfraStrata's proposed underground gas storage facility at Islandmagee in Co Antrim.
Mr Wood added: "This acquisition is a function of deep operational synergies between the various business segments of the company, with Harland and Wolff underpinning the construction economics of the Islandmagee gas storage project and other future projects.
"We are delighted to be able to retain 100% of personnel who did not opt to take voluntary redundancy earlier this year.
"Our Islandmagee gas storage project will benefit greatly from their expertise in the energy sector, both technically and economically, and we look forward to growing the workforce significantly in the coming years.
"While our core priority will be to deliver our flagship project in Islandmagee, we believe there are opportunities to welcome potential new clients due to the diverse skill set at the facility.
"This acquisition will clearly provide substantial advantages through vertical integration in addition to demonstrating our commitment to the Northern Irish economy, particularly in the post-Brexit era."