Two of the three BiFab engineering yards have been brought out of administration.
InfraStrata has taken over steel-fabrication sites in Methil, Fife, and Arnish on the Isle of Lewis, and will run them under the Harland & Wolff brand.
However, the firm has not bought the BiFab yard in Burntisland, Fife, as part of the £850,000 deal.
InfraStrata said 29 staff who are currently on furlough would return to duty to get operations under way.
It wants to focus on wind-farm projects and shipbuilding.
BiFab was put into administration last year while owned by the Scottish Government and a Canadian firm after failing to secure key contracts.
John Wood, chief executive of InfraStrata, said: “I am very pleased to have completed the acquisition of the assets of BiFab, which is in keeping with our stated strategy of capitalising on complementary opportunities when they present themselves.
“With this acquisition, we now have a footprint in Scotland, which is the hotbed for major wind-farm projects as well as for shipbuilding programmes.”
The takeover was welcomed by union leaders, who urged the Scottish and UK governments to show support for the sector, having blamed them for the administration.
In a joint statement, Unite Scotland secretary Pat Rafferty and GMB Scotland secretary Gary Smith said: “The announcement by InfraStrata that two of the BiFab yards will be bought out of administration is welcome news.
“It is also testimony to our members and their communities who have fought hard to keep these yards alive.
“We look forward to working with the company to ensure it is primed to win contracts for the offshore wind sector, and to having a positive working relationship underpinned by the Fair Work principles.
“We have always believed that the BiFab yards, and indeed yards and ports all over Scotland, are uniquely placed to capture the benefits of the offshore wind sector.
“However, the story so far has been one of government failure – thousands of jobs and billions of pounds have been outsourced around the world when Scottish communities should have been benefitting from these contracts.
“Now the Scottish and UK governments have been given a reprieve and they need to step-up and support the new ownership.”
The Scottish Government said it “looked forward” to working with the yards’ new owner.
Economy secretary Fiona Hyslop said: “This is a welcome development for the future of the workforce. The Scottish Government’s priority has been to support BiFab’s workers and I welcome the announcement that a buyer has been found.
“The workforce has an important role to play in the future of manufacturing in Scotland and I look forward to working with the new owner as it forges a new future for the company.
“This is welcome news for the local communities in Fife and the Western Isles.
“The Scottish Government will also engage with Forth Ports, the owner of the Burntisland yard, to help secure the best possible outcome for that yard.”
Scottish Liberal Democrat leader and Fife MSP Willie Rennie said: “The purchase of the BiFab assets at Methil and Arnish could be good news for workers, but we need to be cautious until we see the full plans, investment and commitment from the new owners InfraStrata.
“Given sight of those plans, we of course stand ready to support the recovery and growth of these infrastructure assets.
“The potential is great with all the new wind farms on the verge of construction off the shores of Scotland, but the yards need significant investment to make them competitive with yards from the Far East.”
Scottish Labour economy spokesman Alex Rowley said: “It is of the upmost importance that the new employers engage with the trade unions and ensure that fair work values underpin the futures of the sites.”