Indian conglomerate Tata ceased production at its Dalzell steel plate mill in Motherwell, North Lanarkshire, and the Clydebridge plant in nearby Cambuslang in 2015 with the loss of 270 jobs.
The plants were bought by metals firm Liberty House earlier this year, and Ms Sturgeon officially marked the restart of the Dalzell steel mill on Wednesday morning.
Liberty House said many of the 120 staff at the plant are former employees, and it hopes to increase employment to 200 within 18 months.
Jon Bolton, chief executive of Liberty Steel UK Plates and UK Steel Development, said the reopening of the plant is “hugely important” to the steel industry in Scotland.
He said: “Without it restarting, there wouldn’t be a steel industry in Scotland. I think it is hugely advantageous.
“As the First Minister said today, it’s not just about boosting the steel industry, it’s about the economy. It’s expected to bring in another £15 million a year to the local economy.
“Today was the day we said we would start production and we are doing so with a vengeance. We intend to ramp up production to 150,000 tonnes a year.”
He said he is “confident” Clydebridge will also reopen in the “near future”, adding that other potential uses such as for manufacturing towers for wind turbines are under consideration for that plant.
Ms Sturgeon was given a tour of the Dalzell mill and and met workers and apprentices before the plant was blessed in a traditional Indian ceremony.
The First Minister said: “This is a fantastic day for Dalzell workers, for Motherwell and for Scotland’s steel industry.
“Restarting steel production has only been possible thanks to the tremendous team effort of everyone involved in the steel taskforce to find a viable future for this site, meaning workers here in Lanarkshire can once again produce world-class products.
“Liberty House are seizing an exciting opportunity and the Scottish Government and its agencies will continue to work with Sanjeev Gupta and his team to ensure a successful future in Scotland.”
Mr Gupta, the Liberty House Group executive chairman, paid tribute to the support of the Scottish Government and Scottish Enterprise in helping the company rescue the plate works.
Scottish ministers played a key role in the deal through a ‘’back to back’’ agreement involving the Government buying the plants from Tata and immediately selling them on to Liberty, with the sale completed under the same terms with no cost to the taxpayer.
Mr Gupta said: “There is an impressive spirit of partnership here and a determination to give the Scottish steel industry a real future. From our side we promised we would get this important plant open again by the autumn and today we are proud to be fulfilling that promise.”
He said the firm sees “great opportunities for investment in Scotland and regard this as a very fertile business environment”.