Sanjeev Gupta, executive chairman of the Liberty House Group, said a “new era” for the industry had begun as a result of the deal.
Six months after the struggling Indian conglomerate Tata Steel announced it was mothballing the two sites with the loss of 270 jobs, it handed the keys for them to Liberty House.
• READ MORE: Tata to hand over Scottish steel works to new owner
At the Dalzell plant in Motherwell, North Lanarkshire, a flag with the Tata logo was removed and replaced with one bearing the name Liberty Steel.
With the Scottish Government having played a key role in the deal, First Minister Nicola Sturgeon and enterprise minister Fergus Ewing both watched the ceremony.
Afterwards, Ms Sturgeon urged the UK and Welsh governments to step up efforts to save the giant Port Talbot steel works in South Wales.
Tata will begin the sale process for that site – which is the largest steel plant in the UK – on Monday.
Liberty House has been involved in talks with Tata about the future of Port Talbot but Mr Gupta would only say these were at an early stage, adding: “There is a lot of work to do, it is early days there and it is a massive undertaking.”
The future of the two Scottish plants was secured last month thanks to a back-to-back agreement which involved the Scottish Government buying them from Tata Steel and immediately selling them on to Liberty.
Ms Sturgeon said: “If there is any learning or experience we have got here that can be brought to bear in trying to secure a future for Port Talbot, we will happily share that.
“If there’s anything at all that could be done it should be done. Steel is too strategically important an industry to allow it to go to the wall.
“We all want to see the same kind of hopeful future for Port Talbot as we’re seeing for the Scottish plants today.”
Mr Gupta said the handover ceremony for the two Scottish works marked “the beginning of a new era for these plants, for Scottish steel and for British steel as a whole”.